KTM Motorcycle 50 SX User Manual
OWNER’S MANUAL 2008  
50 SX JUNIOR  
50 SX  
3211222en  
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INTRODUCTION »  
Now you own a modern motorcycle that you and your youngster will certainly enjoy, provided that you serv-  
ice and maintain it properly.  
Please insert the serial numbers of the motorcycle below  
Chassis number  
Engine number  
1
Stamp of dealer  
All information contained is without obligation. KTM-Sportmotorcycle AG particularly reserves the right  
to modify any equipment, technical specifications, prices, colors, shapes, materials, services, service work,  
constructions, equipment and the like so as to adapt them to local conditions or to cancel any of the  
above items, all without previous announcement and without giving reasons. KTM may stop manufactur-  
ing certain models without previous notice. KTM shall not be held liable for any deviations of availabil-  
ity and/or ability to deliver, illustrations, descriptions, printing and/or other errors. The illustrated models  
partly contain extra equipment, which is not applied to standard models.  
© 2007 by KTM-SPORTMOTORCYCLE AG, Mattighofen AUSTRIA; All rights reserved; Reprint, also in  
extracts, with written allowance of KTM-SPORTMOTORCYCLE AG, Mattighofen only.  
In accordance with the international quality management ISO 9001 standard, KTM uses  
quality assurance processes that lead to the highest possible product quality.  
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IMPORTANT INFORMATION »  
INTENDED PURPOSE  
KTM mini-sports motorcycles are designed and constructed to resist the usual wear and tear of normal  
use in competitions.  
The motorcycles comply with the regulations and categories currently in effect with the leading interna-  
tional motorcycle associations.  
OWNER’S MANUAL  
Please read this manual thoroughly before letting your youngster ride the motorcycle for the first time.  
This manual contains important information and recommendations that will help you and your youngster  
to operate and handle the motorcycle properly. In the interest of everybody involved, we urge you to pay  
particular attention to instructions and information marked as follows:  
– Ignoring these instructions can be dangerous to life and limb!  
2
– Ignoring these instructions may damage parts of the motorcycle or impair the motorcycle's  
traffic safety!  
This manual contains important information on the operation and maintenance of your new KTM motor-  
cycle. It went to press describing your model’s latest state of development. Nevertheless, the descriptions  
may deviate slightly from the current design as our motorcycles are permanently improved.The Owner's  
Manual is an integral part of the motorcycle and must be handed over to the new owner when the motor-  
cycle is sold.  
SERVICE  
Observance of the service, maintenance and tuning instructions for the engine and chassis specified in  
the Owner's Manual is a prerequisite for faultless operation and the avoidance of premature wear. An  
improperly tuned chassis can lead to damage and breakage of the chassis components (see chapter on  
checking the basic chassis setting).  
The use of the motorcycle under extreme conditions, e.g. on extremely muddy and wet terrain, can lead  
to higher than average wear on components such as the drive train or the brakes. In this case it may  
become necessary to service or replace wear parts before the service limit specified in the maintenance  
schedule has been reached.  
We expressly point out that work marked with an asterisk (*) in the chapter "Maintenance work on the  
chassis and engine" must be performed by a KTM workshop. If maintenance work should become neces-  
sary during a competition, it must be performed by a trained mechanic.  
Please strictly observe the prescribed running-in periods and inspection and maintenance intervals.  
Compliance with these instructions will significantly prolong the life of your motorcycle.  
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IMPORTANT INFORMATION »  
WARRANTY  
The service work specified in the "Lubrication and Maintenance Schedule" must be performed by a KTM  
workshop and recorded in the service manual otherwise claims under the warranty shall become void.  
No claims can be filed under the warranty for damage or consequential damage caused by manipulations  
or conversions to the motorcycle.  
AUTOMOTIVE FLUIDS  
The fuels and lubricants specified in the Owner's Manual or automotive fluids with equivalent specifica-  
tions must be used in accordance with the maintenance schedule.  
SPARE PARTS, ACCESSORIES  
For the safety of your child, only use spare parts and accessories approved by KTM. KTM shall not assume  
any liability for other products or consequential damage resulting from the use of such products.  
When special needs arise, please contact a KTM dealer, who will seek the assistance of the KTM importer  
if necessary.  
SAFETY  
3
Parents should keep in mind that the safety of their youngsters always depends on the efforts made by  
the parents to ensure that the motorcycle is kept in good working order and only used on safe terrains.  
Nevertheless, driving the motorcycle, like driving any other vehicle, involves a potential risk. Therefore,  
please make sure that all fundamental precautions are taken. Please also read the „INFORMATION ON  
SAFE DRIVING FOR PARENTS“ on page 4.  
TRANSPORT  
When transporting your motorcycle, secure it with elastic straps or other mechaical devices in an upright  
position. Be sure that the fuel tap is closed. If the motorcycle topples over, fuel can flow out of the car-  
buretor or fuel tank.  
ENVIRONMENT  
Riding an off-highway motorcycle is a wonderful form of outdoor recreation and we certainly hope that  
you and your youngsters will enjoy it to the full. However, this enjoyable outdoor activity can cause envi-  
ronmental problems or lead to conflicts with other people. Responsible use of the motorcycle will prevent  
such problems and conflicts. You can contribute to securing the future of motorcycling by making sure  
that you and your youngsters only use the motorcycle within the limits established by the applicable laws,  
making environmental protection one of your top priorities and never violating other people’s rights.  
In this spirit, we hope that you and your youngsters will always safely enjoy your motorcycle!  
KTM-SPORTMOTORCYCLE AG  
5230 MATTIGHOFEN, AUSTRIA  
Attachments: 1 spare parts manual chassis & engine  
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IMPORTANT INFORMATION FOR PARENTS ABOUT SAFE DRIVING »  
KTM mini motorcycles are off-road motorcycles designed for one person only. They are not allowed on  
public roads.  
The vehicle dimensions and components are designed for children from 4 to 10 years of age with a  
maximum weight of. 35 kg (78 lbs) and a maximum height of 130 cm (51 in).  
4
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Have your youngster wear proper protective gear whenever he or she rides the motorcycle: helmet, eye  
protection, chest, back, arm and leg protectors, gloves and boots. To set a good example, be sure to  
wear protective gear yourself whenever riding a motorcycle!  
Before your youngster takes his or her first ride, explain how each of the controls works and check if  
your youngster has understood what you explained. We recommend to review the entire owner’s man-  
ual with your youngster item by item, paying particular attention to the specially marked warnings and  
pointing out the danger of injury.  
–
–
–
–
–
–
Instruct your youngster about riding and falling techniques, explain how the motorcycle will respond  
to shifting of the rider’s weight, etc.  
Before starting the motorcycle for the first time check whether the basic fork and shock absorber  
settings are suitable for your child's weight (see chapter on checking the basic chassis setting)  
Before using the motorcycle you should always check all components for proper operation (see maine-  
nance schedule). Have your youngster perform these technical checks himself / herself as well.  
Whenever you go for a ride with your youngster, keep in mind that the speed should be adjusted to  
your youngster and not the other way around.  
Your youngster must understand that all instructions he or she receives from you or any other super-  
vising adult must be followed.  
Your child must be physically ready to ride a motorcycle. This means that he or she must at least be  
able to ride a bicycle. Being good at sports that require fast reactions is an additional advantage. Your  
youngster should be strong enough to pick up the motorcycle after a fall.  
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Never demand too much of your youngster. Give him or her time to get used to the motorcycle and to  
improve his / her riding skills. Do not even consider letting your youngster participate in a race before  
his / her physical condition, riding skills and motivation have sufficiently developed.  
Explain to your youngster that he / she should always adjust his / her riding speed to the local condi-  
tions as well as to his / her own riding skills and that excessive speed can cause falls and severe  
injuries. Always keep in mind that youngsters tend to underestimate dangers or fail to recognize them  
altogether. The riding speed must be reduced, in particular, on unknown terrain.  
Never let your youngster ride the motorcycle without supervision. An adult should always be present.  
The motorcycle is designed for one rider only. Your youngster is not allowed to transport a passenger.  
When you go for a ride, somebody at home should always know where you are going and when you  
will be back. This makes it easier to send you help, should problems occur.  
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TABLE OF CONTENTS »  
Page  
Page  
Changing spring preloading of the shock absorber . . .20  
IMPORTANT INFORMATION FOR PARENTS  
ABOUT SAFE DRIVING . . . . . . . . . . . . . . . . . . . . . . . . .4  
Check chain tension . . . . . . . . . . . . . . . . . . . . . . . .20  
Correct chain tension . . . . . . . . . . . . . . . . . . . . . . .20  
Chain maintenance . . . . . . . . . . . . . . . . . . . . . . . . .20  
General information about KTM disc brakes . . . . . . .21  
Setting the basic position and play of the hand brake lever . .21  
Checking the brake fluid level/ refilling . . . . . . . . . . .22  
Checking front brake pads . . . . . . . . . . . . . . . . . . . .22  
Replacing the front brake pads . . . . . . . . . . . . . . . .22  
Changing the basic position of the foot brake lever  
SERIAL NUMBER LOCATIONS . . . . . . . . . . . . . . . . . . . .6  
Chassis number . . . . . . . . . . . . . . . . . . . . . . . . . . . .6  
Engine number . . . . . . . . . . . . . . . . . . . . . . . . . . . .6  
OPERATION INSTRUMENTS . . . . . . . . . . . . . . . . . . . . .7  
Throttle grip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7  
Hand brake lever . . . . . . . . . . . . . . . . . . . . . . . . . . .7  
Short circuit button . . . . . . . . . . . . . . . . . . . . . . . . .7  
Filler cap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7  
Fuel tap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7  
Choke (Dell’Orto carburetor PHVA 14 DS) . . . . . . . . . .8  
Choke (Dell’Orto carburetor PHBG 19 BS) . . . . . . . . .8  
Kickstarter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8  
Foot brake lever . . . . . . . . . . . . . . . . . . . . . . . . . . . .8  
Side stand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8  
Plugin - Stand (50 SX) . . . . . . . . . . . . . . . . . . . . . . .9  
Rebound damping function of the shock absorber . . . .9  
General Tips and Warnings for starting the motorcycle . .10  
Instructions for the first ride . . . . . . . . . . . . . . . . . .10  
Running in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10  
Driving instructions . . . . . . . . . . . . . . . . . . . . . . . . .11  
What you should check before each start . . . . . . . . .11  
Starting when the engine is cold . . . . . . . . . . . . . . .12  
Starting when the engine is warm . . . . . . . . . . . . . .12  
What to do when the engine is “flooded” . . . . . . . . .12  
Starting off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12  
Driving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12  
Refueling, fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . .13  
Braking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13  
Stopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13  
(50 SX Junior) . . . . . . . . . . . . . . . . . . . . . . . . . . . .23  
Adjusting the control cable on the rear wheel (50 SX Junior) . .23  
Checking the rear brake linings for wear (50 SX Junior) . .23  
Drum brake maintenance (50 SX Junior) . . . . . . . . .23  
Changing the basic position of the brake lever (50 SX) . .23  
Checking the rear brake fluid level (50 SX) . . . . . . . .23  
Refilling the rear brake fluid reservoir (50 SX) . . . . . .24  
Checking rear brake pads (50 SX) . . . . . . . . . . . . . .24  
Replacing the rear brake pads (50 SX) . . . . . . . . . . . .24  
Removing and mounting the front wheel . . . . . . . . . .25  
Removing and mounting the rear wheel . . . . . . . . . .25  
Tires, air pressure . . . . . . . . . . . . . . . . . . . . . . . . . .26  
Checking spoke tension . . . . . . . . . . . . . . . . . . . . .26  
Cooling system . . . . . . . . . . . . . . . . . . . . . . . . . . . .26  
Checking coolant level . . . . . . . . . . . . . . . . . . . . . .27  
Cleaning the air filter . . . . . . . . . . . . . . . . . . . . . . .27  
Exhaust system . . . . . . . . . . . . . . . . . . . . . . . . . . .27  
Changing the seat height . . . . . . . . . . . . . . . . . . . . .28  
Adjusting the throttle cable . . . . . . . . . . . . . . . . . . .28  
Adjusting the idle speed (Dell’Orto PHVA 14 DS) . . .28  
Adjusting the idle speed (Dell’Orto PHBG 19 BS) . . .28  
Checking the gear oil level . . . . . . . . . . . . . . . . . . .29  
Changing gear oil . . . . . . . . . . . . . . . . . . . . . . . . . .29  
Adjusting the centrifugal clutch . . . . . . . . . . . . . . . .30  
5
PERIODIC MAINTENANCE SCHEDULE . . . . . . . . . . . . .14  
TROUBLE SHOOTING . . . . . . . . . . . . . . . . . . . . . . . . .32  
CLEANING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34  
STORAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34  
TECHNICAL DATA – ENGINE . . . . . . . . . . . . . . . . . . . .35  
TECHNICAL SPECIFICATIONS - CHASSIS . . . . . . . . . . .36  
HEAD WORD INDEX . . . . . . . . . . . . . . . . . . . . . . . . . .37  
MAINTENANCE WORK ON CHASSIS AND ENGINE . . . .16  
Removing the seat . . . . . . . . . . . . . . . . . . . . . . . . .16  
Checking and adjusting the steering head bearing  
(50 SX Junior) . . . . . . . . . . . . . . . . . . . . . . . . . . . .16  
Checking and adjusting the steering head bearing  
(50 SX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17  
How to change the handlebar position . . . . . . . . . . .17  
Basic suspension setup for the weight of the driver . .18  
To determine the sag of the shock absorber . . . . . . . .18  
To determine the sag of the telescopic fork . . . . . . .18  
Telescopic fork maintenance . . . . . . . . . . . . . . . . . .19  
Changing the telescopic fork oil . . . . . . . . . . . . . . . .19  
Cleaning the dust scrabbers of the telescopic fork . . .20  
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SERIAL NUMBER LOCATIONS »  
Chassis number  
The chassis number is located on the type plate on the steering head. Enter  
this number in the field on page no 1.  
Engine number  
The engine number is stamped into the right half of the engine case next to  
the kickstarter. Enter this number in the relevant field on page 1.  
6
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OPERATION INSTRUMENTS »  
Throttle grip  
The throttle grip is located on the right side of the handlebars. It is used to  
reduce the engine speed and, thus, the driving speed.  
Hand brake lever  
The hand brake lever is located on the right side of the handlebars and  
actuates the front wheel brake. The basic position can be adjusted to fit your  
child's hand.  
7
Short circuit button  
The short circuit button [1] turns off the engine. When pressing this button,  
the ignition circuit is short-circuited.  
1
Filler cap  
To open it: turn filler cap counter-clockwise.  
To close it: put filler cap back on and tighten it by turning it clockwise.  
2
Install tank breather hose [2] without kinks.  
Fuel tap  
The fuel tap [3] is located at the front of the motorcycle on the left side of  
the tank.  
Opening the fuel tap: Turn the knob all the way to the left.  
Closing the fuel tap: Turn the knob all the way to the right.  
3
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OPERATION INSTRUMENTS »  
Choke Dell’Orto carburetor PHVA 14 DS (50SX Junior)  
Choke lever [1] is mounted to the right side of the carburetor. If you move  
the choke lever up to the stop, a hole is opened in the carburetor through  
which the engine can draw in additional fuel. This results in a "rich" fuel-air  
mixture required for a cold start.  
Moving the choke lever back closes the hole in the carburetor again.  
1
Choke Dell’Orto carburetor PHBG 19 BS (50 SX)  
Choke control knob [2] is mounted to the left side of the carburetor. If you  
pull the choke control knob up to the stop and turn it 90º, a hole is opened  
in the carburetor through which the engine can draw additional fuel. This results  
in a "rich" fuel-air mixture required for a cold start.  
Turning back the choke control knob returns the knob to the starting position  
and closes the hole in the carburetor again.  
2
8
Kickstarter  
The kickstarter is mounted on the right side of the engine. Its upper part can  
be swivelled.  
Foot brake lever  
The foot brake lever is located in front of the right footrest. The basic posi-  
tion can be adjusted to the seating position (see maintenance work).  
Side stand (50 SX Junior)  
Use your foot to swing the side stand forwards to the stop. Make sure it rests  
securely on solid ground.  
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OPERATION INSTRUMENTS »  
Plugin - Stand (50 SX)  
A socket is provided on the left side of the frame for the plug-in stand [1]  
included in the scope of supply.  
1
Rebound damping function of the shock absorber  
By using the adjusting screw [2], the degree of damping of the rebound can  
be adjusted. Turn the knob clockwise to increase damping, turn it counter-  
clockwise to reduce damping during rebounding.  
STANDARD ADJUSTMENT:  
– turn the adjusting screw clockwise to the stop.  
– then turn the adjusting screw counterclockwise, counting the number of  
clicks that corresponds to the respective type of shock absorber.  
50 SX Junior: . . . . . . . . . .12  
50 SX: . . . . . . . . . . . . . . .10  
2
9
– Never turn the setting wheel more than two clicks between two test rides.  
– Do not try to disassemble the shock absorber or to perform maintenance  
work yourself. Danger of injury!  
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GENERAL TIPS AND WARNINGS FOR STARTING THE MOTORCYCLE »  
Instructions for the first ride  
Running in  
– Make sure the work for the "pre-delivery inspection" was per-  
formed by your authorized KTM workshop. The DELIVERY  
CERTIFICATE and SERVICE MANUAL will be handed over  
when you pick up your vehicle.  
– Before your youngster takes his or her first ride, explain how  
each of the controls works and check if your youngster has under-  
stood what you explained. We recommend to review the entire  
owner’s manual with your youngster item by item, paying par-  
ticular attention to the specially marked warnings and point-  
ing out the danger of injury.  
– Adjust the basic position of the hand brake lever to fit the size  
of your child's hand. You child should of course wear gloves.  
Adjust the foot brake lever to your child's seating  
position.  
– Even very precisely machined sections of engine components  
have rougher surfaces than components which have been slid-  
ing across one another for quite some time. Therefore, every  
engine needs to be broken in. Do not load the engine to the  
power limit during the first half hour for this reason.  
– Apply low but changing loads for running-in.  
– NO FULL-LOAD OPERATION DURING THE FIRST HALF HOUR!  
– Have your youngster wear proper protective gear whenever he  
or she rides the motorcycle: helmet, eye protection, chest, back,  
arm and leg protectors, gloves and boots. To set a good exam-  
ple, be sure to wear protective gear yourself whenever riding a  
motorcycle!  
10  
– To prevent injury, teach your youngster the basic riding skills  
on soft ground, e.g. on a meadow or in the garden. Be sure  
that there is room enough to maneuver, and that no other rid-  
ers are close.  
– To ensure that your youngster gets the feel of the brakes, have  
your youngster operate the brakes while you push the motor-  
cycle. Do not start the engine before your youngster has learned  
to apply both brakes with appropriate pressure.  
– Now your youngster must get the feel of the throttle. Start the  
engine, hold the motorcycle and have your youngster slowly  
open the throttle. Then, your youngster can take his/her first  
ride. Initially, your youngster should ride back and forth between  
two persons who help the young rider to stop the motorcycle.  
However, you should also teach your youngster how to stop the  
motorcycle himself/herself.  
– To improve his/her riding skills, your youngster should practise  
to ride the motorcycle standing on the footpegs or riding at the  
slowest possible speed. Additionally, you can arrange a series  
of obstacles and have your youngster drive around them, etc.  
– Tell your youngster to look 3-10 m ahead, depending on the  
speed, to recognize and avoid obstacles. When riding through  
curves, the rider should also look far ahead into the curve.  
– Pay attention to running-in procedure.  
– The motorcycle has a centrifugal clutch. The motorcycle begins  
to move as soon as the throttle is opened.  
– Always apply the front brake when starting the engine and release  
the brake slowly when the engine is running. An activated  
choke increases the idle speed of the engine, the centrifugal  
clutch thus beginning to engage. Therefore, the motorcycle can  
begin to move when the brake levers are released.  
– When the engine speed drops to the level at which the cen-  
trifugal clutch disengages, braking with the engine is no longer  
possible and the motorcycle can only be slowed down using  
the brakes.  
– Your child should never drive faster than its skills and the ter-  
rain permit.  
– Never let your child drive its motorcycle unchaperoned.  
– Replace the helmet visor or goggle glasses early enough. When  
light shines directly on a scratched visor or goggles, you will  
be practically blind.  
– Only use accessory parts recommended by KTM.  
– Never leave your motorcycle without supervision as long as the  
engine is running.  
– KTM mini models are designed for one person only. Passengers  
are not allowed.  
– These models do not comply with the regulations and safety  
standards established by the law. Therefore, they are not per-  
mitted on public roads.  
– Always keep in mind that other people feel molested by exces-  
sive noise.  
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DRIVING INSTRUCTIONS »  
What you should check before each start  
When you start off, the motorcycle must be in a perfect technical condition.  
For safety reasons, you should make it a habit to perform an overall check of  
your motorcycle before each start.  
The following checks should be performed:  
1
CHECK TRANSMISSION OIL LEVEL  
A lack of gear oil leads to premature wear and finally results in destruc-  
tion of the gear wheels.  
2
FUEL  
11  
Check that there is sufficient fuel in the tank; when closing the filler cap,  
check that the tank venting hose is free of kinks.  
3
4
COOLING FLUID  
Check the level of cooling fluid when the engine is cold.  
CHAIN  
A loose chain was fall off the chain wheels; an extremely worn chain may  
tear, and insufficient lubrication may result in unnecessary wear of the  
chain and chain wheels.  
5
6
TIRES  
Check for damaged tires. Tires showing cuts or dents must be replaced.  
Also check the air pressure. Insufficient tread and incorrect air pressure  
deteriorate the driving performance.  
BRAKES  
Check for proper functioning, check brake fluid level in the tank. The  
tank is designed such that it does not need to be refilled, even if the  
brake shoes are worn. If the brake fluid falls below the minimum level,  
the brake system is either leaking or the brake shoes are completely worn  
out. Have the brake system checked at a KTM workshop to avoid brake  
failure. Also have the condition of the brake hose and the brake lining  
thickness checked.  
Check the play of the hand brake lever and foot brake lever.  
7
THROTTLE CABLE  
Check the throttle cable for proper adjustment and smooth operation.  
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DRIVING INSTRUCTIONS »  
Starting when the engine is cold  
1
2
3
4
5
Open fuel tap [1].  
Operate the choke [2].  
Kick the side up all the way or remove the plug-in stand.  
Apply the front brake.  
Operate the kickstarter, depressing it all the way, without opening the throt-  
tle.  
– When starting the engine, put on motorcycle boots in order to avoid  
injuries. You may slip off the kickstarter, or the engine may kick back if  
you do not kick hard enough.  
1
– Do not start the engine and allow it to idle in a closed area. Exhaust fumes  
are poisonous and can cause loss of consciousness and death. Always pro-  
vide adequate ventilation while the engine is running.  
12  
Don’t ride your motorcycle with full load and high revs when engine is cold.  
Because the piston is warming up faster than the water cooled cylinder, it can  
cause engine damage.  
NOTE:  
2
The highly inflammable components in modern fuels volatilize if left stand-  
ing for longer periods of time. If the motorcycle has not been used for over  
1 week, the fuel should be drained from the float chamber. The engine will  
start up immediately if the float chamber is filled with fresh, ignitable fuel  
Starting when the engine is warm  
1
2
3
4
Open fuel tap [1].  
Kick the side up all the way or remove the plug-in stand.  
Apply the front brake.  
Operate the kickstarter, depressing it all the way, without opening the throt-  
tle.  
What to do when the engine is “flooded”  
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Close fuel tap [1].  
Applying the front brake.  
Start engine with full throttle. If necessary, unscrew spark plug and  
dry it.  
4
Once the engine is running, open fuel tap again.  
Starting off  
Slowly release the brake lever while simultaneously opening the throttle.  
Always make sure the side stand is kicked all the way up or the plug-in stand  
removed before you let your child drive off. The motorcycle could run out of  
control if the stand touches the ground.  
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DRIVING INSTRUCTIONS »  
Driving  
The engine speed, and thus the driving speed, are regulated by  
– Close the fuel tap when leaving the motorcycle. Otherwise the  
carburetor may get flooded and fuel will enter the engine.  
– The side stand or plug-in stand is designed to hold the weight  
of the motorcycle only. By sitting on the motorcycle, your child  
will put additional weight on the side stand, possibly causing  
the side stand or frame to be damaged or the motorcycle to  
fall down.  
the throttle grip.  
The choke must always be deactivated as soon as the engine has  
warmed up.  
– After falling with the motorcycle, check all its functions thor-  
oughly before using it again.  
– A bent handlebar must always be replaced. Never try to  
straighten the handlebar because this will cause it to lose its  
stability.  
Refueling, fuel  
Oil (high-grade two-stroke engine oil) must be mixed with the fuel  
(ROZ 95) at a mixing ratio of 1:60.  
13  
Fuel and engine oil should only be mixed immediately before  
use.KTM recommends Motorex 2T Cross Power.  
– Driving a cold engine at high speed will reduce the life of the  
engine. We recommend to warm the engine up at a medium  
engine speed for several minutes before switching to full load.  
– Never tilt the motorcycle over the side stand to warm up the  
engine. The side stand could fold away and the motorcycle run  
out of control.  
– In the event that, while your child is riding on the motorcycle,  
you notice any unusual operation-related noise, your child  
should stop immediately, turn the engine off, and contact an  
authorized KTM dealer.  
Gasoline is highly flammable and poisonous. Extreme caution  
should be used when handling gasoline. Never refuel the motor-  
cycle near open flames or burning cigarettes. Always switch off  
the engine before refueling. Be careful not to spill gasoline on the  
engine or exhaust pipe while the engine is hot. Wipe up spills  
promptly. If gasoline is swallowed or splashed in the eyes, seek a  
doctor’s advice immediately.  
Braking  
– Only use premium-grade gasoline ROZ 95 mixed with high-  
grade two-stroke engine oil. Other types of gasoline can cause  
engine failure.  
– Only use known brands of high-grade 2-stroke engine oil  
(Motorex 2T Cross Power).  
Close the throttle and squeeze both brake levers simultaneously.  
On sandy, wet or slippery terrain the rear wheel brake should be  
preferred. The brakes should always be operated carefully as  
locking wheels can cause skidding or falls.  
– Not enough oil or low-grade oil can cause erosion of the pis-  
ton. when Using too much oil, the engine may start smoking  
and foul the spark plug.  
– Fuel expands when its temperature rises. Therefore do not fill  
the tank to the top. (see fig.)  
– Brake drum and linings heat up during brake operation, thus  
reducing the effect of the brakes.  
– Wet brakes have reduced brake performance, therefore be sure  
to brake them dry after cleaning.  
– If the resistance of the hand brake lever feels unresponsive,  
something is wrong with the brake system. Have the brake sys-  
tem checked at a KTM workshop before you let your child drive  
the motorcycle.  
40 mm  
Stopping  
Reduce the speed. Immediately before the motorcycle comes to  
a stop, put the left foot down. To turn off the engine, press the  
short circuit button until the engine stops. Close the fuel tap.  
Motorcycles produce great heat during operation. Therefore, keep  
in mind that the engine, the exhaust system and the brakes can  
heat up considerably. Make sure that these parts are not touched  
and always take care, when parking the motorcycle, that other per-  
sons will not burn themselves.  
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PERIODIC MAINTENANCE SCHEDULE »  
50 SX JUNIOR  
50 SX  
A CLEAN MOTORCYCLE CAN BE CHECKED MORE QUICKLY WHICH SAVES MONEY!  
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Check engine for leaks  
Change transmission oil  
Check spark plug, change it if necessary, set electrode gap  
Check the clutch engagement speed  
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Check carburetor for a tight fit at intake flange  
Check intake flange for cracks  
Check idle setting when engine is warm  
Check cooling system for leaks, check quantity of antifreeze  
Check exhaust system for leaks and suspension  
Check actuating cables for damage, smooth operation, and kinkless arrangement, adjust and lubricate  
Clean air filter and air filter box  
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Check brake fluid level, lining thickness, brake discs  
Check the brake line and the brake control cable for damage  
Check/function adjust smooth operation, free travel of handbrake/footbrake levers  
Check screws of brake system for a tight fit  
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Check suspension strut and fork for leaks and a proper function  
Check swinging-fork pivot  
Check/adjust steering-head bearing  
Check all chassis screws for a tight fit (fork plates, axle nuts, swinging-fork pivot, suspension strut)  
Check spoke tension and rim joint  
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Check tire condition and inflation pressure  
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Check chain, chain joint, chain wheels, chain wheel guides for wear, a tight fit, and tension  
Lubricate chain  
Check wheel bearings for play  
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PERIODIC MAINTENANCE SCHEDULE »  
50 SX JUNIOR  
50 SX  
ADDITIONAL SERVICE WORK TO BE PERFORMED UNDER A SEPARATE ORDER  
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Check the reed-type intake valve for wear  
Check the clutch shoes for wear  
Check the clutch drum for wear  
Check the water pump shaft and bearings for wear  
Check the water pump wheel for wear  
Check the cylinder and piston for wear  
Check the eccentricity of the crankshaft journal  
Check the radial clearance of the conrod bearings  
Check the radial clearance of the piston pin main bearing  
Check the crankshaft main bearing for wear  
Replace the crankshaft bearings and conrod bearings  
Check the entire transmission including bearings for wear  
Drain and clean the carburetor's float chamber  
Perform complete fork maintenance  
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Perform complete shock absorber maintenance  
Clean and lubricate the swinging-arm bearing  
Clean and lubricate the steering-head bearing and sealing elements  
Change brake fluid  
15  
NOTE: If the inspection establishes that permissible tolerances are exceeded, the respective components must be replaced.  
The kilometer reading for inspection intervals should not exceed 5 hours.  
Maintenance work performed by your authorized KTM workshop is not a substitute for care and maintenance by the driver!  
NOTE: A service hour counter (item no.: SXS05450600) is available from your KTM dealer for strict observance of the service  
intervals.  
50 SX JUNIOR  
50 SX  
VITAL CHECKS AND CARE PROCEDURES TO BE CONDUCTED BY THE OWNER OR THE MECHANIC  
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Check transmission oil level  
Check cooling liquid level  
Check brake fluid level  
Check brake pads for wear  
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Check brake performance  
Lubricate and adjust actuating cables and nipples  
Remove and clean dust sleeves of telescopic fork at regular intervals  
Clean and lubricate chain, check tension and readjust it if necessary  
Clean air filter and filter box  
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Check tire inflation pressure and wear  
Check fuel line for leaks  
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Drain and clean float chamber  
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Verify smooth operation of all controls  
Treat exposed metal components (except for the brake and exhaust systems)  
with wax-based anti-corrosion agents  
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Check all screws, nuts, and hose clamps for their tight fit at regular intervals  
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Maintenance work and adjustments marked with an asterisk (*) must be performed by an expert. To protect your youngster, always have  
such work performed by a specialized KTM dealer where your motorcycle will be optimally serviced by appropriately qualified, skilled  
staff.  
– When cleaning the motorcycle, do not use a high pressure cleaning unit if possible, otherwise water will penetrate the bearings,  
carburetor, electric connectors, drum brakes, etc.  
– Before cleaning with water, plug the exhaust pipe to prevent water ingress.  
– When transporting your motorcycle, secure it with elastic straps or other mechanical devices in an upright position. Be sure that  
the fuel tap is closed. If the motorcycle topples over, fuel can flow out of the carburetor or fuel tank.  
– Do not use toothed washers or spring rings with the engine fastening screws, as these work into the frame parts and keep working  
loose. Instead, use self-locking nuts.  
– Let your motorcycle cool down before beginning any maintenance work in order to avoid getting burned.  
– Dispose of oils, fatty matters, filters, fuels, washing detergents, etc. properly.  
– Under no circumstances may used oil be disposed of in the sewage system or in the open countryside. 1 liter of used oil contam-  
inates 1,000,000 liters of water.  
16  
Removing the seat  
1
The quick-release mechanism [1] allows removal of the seat without tools.  
Turn the quick-release device approximately 180° counterclockwise, lift the  
rear portion of the seat and pull the seat off backwards.  
When mounting the seat ensure that the hook engages at the tank.  
Checking and adjusting the steering head bearing (50 SX Junior) *  
The steering head bearing should be checked regularly for play. For this  
purpose, jack up the motorcycle by the frame so that the front wheel is in the  
air. Now try to move the fork forward and backward. There should be no clear-  
ance. For readjustment, release the two clamp screws [2] of the top triple  
clamp and the counternut [3]. Turn the adjusting nut [4] until almost no play  
is left. Do not tighten the adjusting nut! Tightening the adjusting nut can  
damage the bearings! Keep in mind that tightening the counternut [3] reduces  
the play of the bearing. Slightly tap the top triple clamp with a rubber ham-  
mer to prevent jamming. Then tighten the 2 clamp screws with 25 Nm.  
3
2
If the steering head bearing is not adjusted to be free of clearance, the motor-  
cycle will exhibit unsteady driving characteristics and can get out of control.  
4
2
3
– The handlebar must move easily. Otherwise the bearings will be damaged.  
– If you drive with play in the steering head bearing for longer periods, the  
bearings and subsequently the bearing seats in the frame will be destroyed.  
At least once a year, the steering head bearings should be smeared with water-  
proof grease (Motorex Long Term 2000).  
4
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Checking and adjusting the steering head bearing (50 SX) *  
The steering head bearing should be checked regularly for play. To check,  
support the motorcycle frame and lift the front wheel off the ground. Now try  
to move the fork back and forth – you should not feel any play. To adjust,  
loosen both clamping screws [1] on the upper triple clamp and loosen the  
steering head screw [2] by a few turns. Lift the triple clamp slightly and turn  
the adjusting nut [3] until hardly any play is left. Never tighten the adjusting  
nut since you might damage the bearing. Tighten the steering head screw to  
a torque of 10 Nm and the 2 clamping screws to 25 Nm.  
2
If the steering head bearing is not adjusted to be free of clearance, the motor-  
cycle will exhibit unsteady driving characteristics and can get out of control.  
1
– The handlebar must move easily. Otherwise the bearings will be damaged.  
– If you drive with play in the steering head bearing for longer periods, the  
bearings and subsequently the bearing seats in the frame will be destroyed.  
3
17  
At least once a year, the steering head bearings should be smeared with water-  
proof grease (Motorex Long Term 2000).  
2
1
3
How to change the handlebar position  
The handlebar position can be readjusted by 22 mm (0.9 in). The upper triple  
clamp [4] includes 2 bores arranged at a distance of 15 mm (0.6 in) from  
one another. The bores at the handlebar support [5] are offset from the  
center by 3.5 mm (0.13 in). Accordingly, you can mount the handlebar in 4  
different positions.  
For this purpose, remove screws [6] of the handlebar clamps and screws [7]  
of the handlebar support. Position handlebar support, and tighten screws [7]  
to 40 Nm. Mount handlebar and handlebar clamps, and tighten screws [6]  
to 20 Nm. The gap between the handlebar support and handlebar clamps  
should be the same size in the front and in the rear.  
6
7
5
3,5 mm  
The screws [7] must be secured with Loctite 243.  
4
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Basic suspension setup for the weight of the driver  
To achieve maximum handling performance and to prevent the telescopic fork  
and shock absorber from being damaged, the basic setup of the suspension  
components must be suitable for your child's weight. At delivery, KTM's mini  
motorcycles are set to accommodate a driver weighing 25 - 30 kg (wearing  
full protective clothing). If your child's weight exceeds or falls short of this  
range, you will need to adjust the spring preload for the telescopic fork and  
shock absorber accordingly.  
A
To adjust, check the sag of the shock absorber and telescopic fork. The motor-  
cycle should be filled up and your child should be wearing full protective  
clothing.  
To determine the sag of the shock absorber  
– Jack up the motorcycle until the rear wheel no longer touches the ground.  
– Measure the vertical distance between the rear wheel axle and a fixed point  
(e.g. a mark on the side cover) and write it down as dimension A.  
– Place the motorcycle on the ground again.  
– Have your child sit on the motorcycle in a normal seating position  
(feet on the footrests) wearing full protective clothing and bounce up and  
down a few times to allow the rear wheel suspension to become level.  
– Holding your child and the bike, have another person measure the  
distance between the same two points with the load on the motorcycle to  
establish dimension B.  
B
B
– The sag is the difference between dimensions A and B.  
EXAMPLE:  
18  
Motorcycle jacked up (dimension A) . . . . . . . . . . . . . . . . . . . . . .400 mm  
Motorcycle on ground with driver seated (dimension B) . . . . . . .– 355 mm  
Sag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 mm  
50 SX Junior shock absorber sag . . . . . . . . . . . . . . . . . 45 mm (± 5 mm)  
50 SX shock absorber sag . . . . . . . . . . . . . . . . . . . . . . 50 mm (± 5 mm)  
If the sag is lower, the spring preload of the shock absorber must be reduced,  
if the sag is higher, the spring preload must be increased (see Changing spring  
preloading of the shock absorber). A harder spring is also available for the  
50 SX (see spare parts catalog).  
C
To determine the sag of the telescopic fork  
– Jack up the motorcycle until the rear wheel no longer touches the ground.  
– Measure the distance between the upper edge of the slider tube and the  
triple clamp and write it down as dimension C.  
– Have your child sit on the motorcycle in a normal seating position  
(feet on the footrests) wearing full protective clothing, and bounce up and  
down a few times to allow the telescopic fork to become level.  
– Holding your child and the bike, have another person measure the  
distance between the same two points with the load on the motorcycle to  
establish dimension D.  
– The sag is the difference between dimensions C and D.  
EXAMPLE:  
Motorcycle jacked up (dimension C) . . . . . . . . . . . . . . . . . . . . . .200 mm  
Motorcycle on ground with driver seated (dimension D) . . . . . . .– 160 mm  
Sag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40 mm  
1
50 SX Junior telescopic fork sag . . . . . . . . . . . . . . . . . 30 mm (± 5 mm)  
50 SX telescopic fork sag . . . . . . . . . . . . . . . . . . . . . . 45 mm (± 5 mm)  
D
If the sag is lower, the spring preload of the telescopic fork must be reduced,  
if the sag is higher, the spring preload must be increased.  
The preload on the fork spring is determined by the length of preload spacer  
[1]. If an adjustment is necessary, demount the fork legs, remove the plugs  
and shorten the pretensioning sleeves or replace with longer ones  
(see maintenance of telescopic fork). Harder fork springs are also available  
for both models (see spare parts catalog).  
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Telescopic fork maintenance *  
The telescopic fork must be serviced at least once a year.  
To service the fork, proceed as follows:  
Prop up the motorcycle under the frame to take the load off the front wheel.  
Disassemble the front wheel, remove screw [1] from the brake caliper and  
unscrew holding clamp. Measure the projection of the fork legs at the upper  
fork stabilizer and make a note of the measurement.  
2
1
Loosen the clamping screws [2] on the fork stabilizers and pull the fork legs  
down out of the fork stabilizers.  
2
1
– Do not operate the hand brake when the front wheel has been dismounted.  
– Make sure the brake disc is always on top when you lay down the wheel,  
otherwise the brake disc can be damaged.  
Clamp the fork leg into a vise (use protective jaws) and remove the  
plugs [3]. Take the preload spacer and the spring out of the fork tube.  
Remove screws [4] at the underside of the slider tubes and pull the fork tubes  
out of the slider tubes.  
3
Remove the dust scrabbers [5].  
19  
Thoroughly clean all parts and check for wear.  
Generously lubricate seals and springs and reassemble the telescopic fork.  
Tighten the screws on the bottom of the sliding tubes to 30 Nm.  
Fill in fork oil and assemble the fork (see below). Degrease the screws on the  
brake caliper and apply Loctite 243. Mount the brake caliper and tighten to  
20 Nm. Mount brake line and holding clamp.  
5
4
Insert fork legs in the fork stabilizers (projection as previously noted) and tighten  
clamping screws to 25 Nm (top) and 10 Nm (bottom).  
Mount front wheel (see chapter: mounting the front wheel).  
The screws [1] must be secured with Loctite 243.  
Changing the telescopic fork oil *  
Remove front wheel and fork legs (see above).  
Remove plugs, preload spacers and springs.  
Drain the fork oil into an appropriate container.  
Clean the dust scrabbers.  
– It is very important to keep the brake disk free from oil and fatty matters.  
Otherwise, the braking effect would be strongly reduced.  
– After working on the brake system, always operate the hand brake lever  
to apply the brake shoes to the brake disk and have a point of pressure.  
Pour 170 cm3 SAE 7.5 fork oil into each fork tube.  
Slide the fork tube all the way into the slider tube.  
Adjust the air-chamber length [A] to 110 mm (4.5 in) by extracting or adding  
fork oil.  
Insert springs and pretensioning sleeves into the fork tube.  
Check O-rings, grease and mount plugs.  
Mount the fork legs, front wheel and brake caliper (see above).  
A
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Cleaning the dust scrabbers of the telescopic fork  
The dust-protection bellows [1] are to remove dust and coarse dirt particles  
from the fork tube. However, after some time, dirt may also get in behind the  
dust-protection bellows. If this dirt is not removed, the oil sealing rings located  
behind it may start to leak.  
For this purpose, use a screwdriver to lift the dust scrabbers out of the  
slider tubes, clean them thoroughly with compressed air, spray the fork tubes  
and dust scrabbers with Universal oil spray (Motorex Joker 440) or engine oil.  
Then, push the dust-protection bellows into the outer tubes by hand.  
1
No oil may reach the front tire or the brake disks since this would consider-  
ably reduce the tire's road grip and the braking effect of the front brake.  
Changing spring preloading of the shock absorber  
This is easily done.  
NOTE: Before changing the spring preload note down the basic setting, e.g.  
how many threads are visible above the adjusting ring.  
2
3
Remove the right side cover.  
Loosen the locking ring [2] with the hook spanner. Change the spring preload  
with the adjusting ring [3] and re-tighten the locking ring [2].  
BASIC SETTING – SPRING PRELOAD:  
50 SX Junior: . . . . . . . . . .5 mm (0.2 in)  
50 SX: . . . . . . . . . . . . . . .3 mm (0.12 in)  
20  
Check chain tension  
Put the motorcycle on the sidestand.  
Chain tension has to be checked close to the lower rear shock mounting [A].  
When pushing the chain upwards, the distance to the swingarm has to be  
10 mm (0.4 in).  
If necessary, correct chain tension.  
10 mm  
A
–
If chain tension is too great, parts within the secondary transmission (chain,  
chain wheels, gear box and rear wheel bearings) will be subjected to unnec-  
essary stress, resulting in premature wear and even chain breakage.  
– Too much slack in the chain, on the other hand, can result in the chain  
jumping off the chain wheels. If this happens, the chain could also block  
the rear wheel or damage the engine. In either case the operator is likely  
to lose control of the motorcycle.  
– Be careful not to get your finger caught between the chain and the rear  
sprocket or other components.  
Correct chain tension  
Release the hexagon nut of the wheel spindle [4] and turn the left and the  
right hexagon nut [5] equally far.  
6
4
6
Before tightening the hexagon nut of the wheel spindle to 40 Nm, ensure that  
the supporting plates [6] are resting against the swing arm. Additionally,  
check that the rear wheel is aligned with the front wheel.  
5
5
Chain maintenance  
For long chain life, good maintenance is very important. Chains without  
O-rings should be cleaned in fireproof solvent regularly and afterwards  
treated with hot grease or chain spray (Motorex Chainlube Racing).  
Keep the rear wheel free of grease! Grease on the rear wheel will significantly  
reduce the grip of the rear tire and the motorcycle could easily get out of  
control.  
When mounting the chain masterlink clip, the closed side of the masterlink  
clip must point in running direction.  
Also check sprockets and chain guides for wear, and replace if necessary.  
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
General information about KTM disc brakes  
BRAKE FLUID RESERVOIRS:  
The brake fluid reservoirs for the front brake is designed such that it does not  
need to be refilled, even if the brake shoes are worn. If the brake fluid level  
drops below the minimum level either the brake system has a leak or the brake  
pads are completely worn.  
In this case, consult an authorized KTM dealer immediately.  
BRAKE FLUID:  
We recommend that you use Motorex DOT 5.1 brake fluid when you refill or  
change the brake fluid. DOT 5. 1 brake fluid has a wet boiling point of 180°C  
/ 356°F (25°C / 45°F higher than DOT 4) and is safer for high performance  
applications. Brake fluid DOT 5.1 is a polyethylene glycol based fluid, amber-  
colored and can be mixed with DOT 4 brake fluid. Do not, in any event, use  
DOT 5 brake fluid. It is based on silicone oil and is dyed purple. KTM motor-  
cycle gaskets and brake hoses are not designed for DOT 5 brake fluid.  
A
Have the brake fluid changed at least once annually. If you wash your motor-  
cycle often, the brake fluid should be changed even more frequently. Brake  
fluid tends to absorb water. Therefore, vapor pockets may form in "old" brake  
fluids even at low temperatures, causing the brake system to fail.  
BRAKE DISC:  
Due to wear, the thickness of the brake disc in the area of the contact  
face [1] of the brake pads decreases. The brake disk must be at least 2.50  
mm thick at the thinnest point [A]. Check the thickness of the brake disk at  
several points.  
1
21  
– A brake disk worn down to less than 2.50 mm is a safety risk. Have the  
brake disk replaced as soon as it reaches the service limit.  
– Have any repairs on the brake system be performed by a KTM dealer.  
BRAKE CALIPERS:  
Secure the screws on the brake caliper with Loctite 243 and tighten to a torque  
of 20 Nm.  
Setting the basic position and play of the hand brake lever *  
You can adjust the basic position of the hand brake lever to fit your child's  
hand by turning stop screw [2]. Afterwards, be sure to adjust the play of the  
hand brake lever to 2 mm (0.08 in)with the adjusting screw [3]. To adjust,  
remove covering cap [4]. Replace the covering cap after making the adjust-  
ment.  
min. 2 mm  
4
2
At the hand brake lever, free travel must at least be 2 mm (0.08 in). Only  
then may the piston in the hand brake cylinder be moved (to be recognized  
by the greater resistance of the hand brake lever). If this free travel is not pro-  
vided, pressure will build up in the braking system, and the front-wheel brake  
may fail due to overheating.  
3
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Checking the brake fluid level / refilling *  
1
The brake fluid reservoir is combined with the hand brake cylinder on the  
handlebar. To check the brake fluid level, press the brake pistons back into  
the basic position. Move the hand brake cylinder in a horizontal position, remove  
the screws [1] and the cover [2] with the diaphragm [3]. The brake fluid level  
should be 5 mm below the upper edge of the reservoir (see drawing),  
otherwise add DOT 5.1 brake fluid (e.g. Motorex Brake Fluid DOT 5.1) up to  
5 mm below the upper edge of the reservoir.  
2
Mount the diaphragm, the cover and the screws and actuate the hand brake  
lever until you feel the point of pressure again. Wipe off any overflowing or  
spilled brake fluid with water.  
3
– Actuate the hand brake lever until you feel the point of pressure again.  
– Never use DOT 5 brake fluid! It is based on silicone oil and of a purple  
color. Seals and brake hoses must be especially adapted to it.  
– Store brake fluid out of reach of children.  
– Brake fluid can cause skin irritation. Avoid contact with skin and eyes. If  
you get brake fluid in your eyes, rinse with plenty of water and consult a  
doctor.  
5 mm  
– Don’t let brake fluid get in contact with paint, it is an effective  
paint remover.  
– Use only clean brake fluid taken from a tightly sealed container.  
22  
Checking front brake pads  
Inspect the brake pads from in front of the vehicle. The linings must be at  
least 1 mm (0.04 in) thick.  
min.  
1 mm  
At their most worn point brake pad linings should not be thinner than 1 mm  
(0.04 in), otherwise they could lead to brake failure. For your own safety don’t  
put off having your brake pads changed.  
If the brake pads are replaced too late so that the lining is partly or entirely  
worn, the steel components of the brake pad will rub against the brake disc,  
thereby imparing the braking effect and destroying the brake disc.  
Replacing the front brake pads *  
Remove the front wheel (see front wheel chapter).  
Press brake shoes apart with a suitable screwdriver to put the brake pistons  
in their basic position.  
Remove the lock washer [4] from the screw as well as fixing screw [5] and  
take the brake shoes out of the brake caliper. Clean brake caliper thoroughly  
with compressed air.  
4
Mount the left brake shoe and fix with screw. Mount the right brake shoe and  
tighten the screw to 4 Nm. Mount the lock washer. Align brake shoes, mount  
front wheel (see chapter: Mounting the front wheel).  
– It is very important to keep the brake disk free from oil and fatty matters.  
Otherwise, the braking effect would be strongly reduced.  
– After assembly, check if circlips have been fitted correctly.  
– Do not unscrew any other screws on the brake caliper or you will have to  
bleed the brake system.  
– After working on the brake system always operate the hand brake lever to  
apply the brake pads to the brake disk and create a point of pressure.  
5
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Changing the basic position of the foot brake lever (50 SX Junior)  
The basic position of the foot brake lever can be changed by unscrewing screw  
[1] and then turning the retainer [2].  
Afterwards, check the setting of the rear wheel brake.  
2
Adjusting the control cable on the rear wheel (50 SX Junior)  
You should be able to press the foot brake lever 5 to 10 mm (0.2-0.4 in)  
before the rear wheel begins to brake.  
The brake control cable is adjusted with adjusting screw [3] on the brake anchor  
cover. First loosen lock nut [4] and then tighten again.  
1
2
5-10 mm  
After making adjustments, always make sure the wheel turns freely.  
Checking the rear brake linings for wear (50 SX Junior)  
The brake linings must be replaced when the distance between the hub brake  
lever and the cable support, measured with the brake lever squeezed, is less  
than 50 mm (2 in) (see illustration).  
min 50 mm  
If the brake linings are replaced too late, i.e. when the lining is partly or fully  
worn away, the metal shoes will rub against the brake drum, thus reducing  
the braking effect and destroying the brake drum.  
3
4
23  
Drum brake maintenance (50 SX Junior)  
Drum brake maintenance is limited to occasional blowing out of the brake  
drum and brake shoes. Brake drum and brake linings can be slightly  
roughened with an abrasive tape.  
Changing the basic position of the foot brake lever (50 SX) *  
The basic setting of the foot brake pedal can be changed by turning the end  
stop roller [5]. Using the push rod [6], the free play on the foot brake pedal  
must be set.  
5
Measured on the outside, the foot brake pedal must have 3-5 mm of free play,  
before the push rod can move the piston in the brake cylinder (to be recog-  
nised from the resistance on the foot brake pedal)  
6
3-5 mm  
Checking the rear brake fluid level (50 SX)  
The reservoir for the rear disk brake is on the right side of the motorcycle on  
the rear brake cylinder.  
No air bubble should be visible in inspection glass [A] when the vehicle is  
parked in a vertical position.  
If the brake fluid level drops below the upper edge of the inspection glass,  
this indicates that the brake system is either leaking or the brake shoes com-  
pletely worn.  
A
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Refilling the rear brake fluid reservoir (50 SX) *  
1
Remove the screws [1] and take off the cover [2] and diaphragm [3].The brake  
pistons must be pushed back to their basic position. Fill DOT 5.1 brake fluid  
(e.g. Motorex Brake Fluid DOT 5.1) up to 10 mm under the upper edge of the  
reservoir.  
Remount the diaphragm, cover and screws and actuate the foot brake lever  
until you feel the point of pressure again. Wipe any overflowing or spilled brake  
fluid off with water.  
2
3
– Actuate the foot brake lever until you feel the point of pressure again.  
– Never use DOT5 brake fluid! It is based on silicone oil and of a  
purple color. Seals and brake hoses must be especially adapted to it.  
– Store brake fluid out of reach of children.  
– Brake fluid can cause skin irritation. Avoid contact with skin and eyes. If  
you get brake fluid in your eyes, rinse with plenty of water and consult a  
doctor.  
– Don’t let brake fluid get in contact with paint, it is an effective paint remover.  
– Use only clean brake fluid taken from a tightly sealed container.  
24  
(50 SX)  
Checking the rear brake pads  
The brake pads can be inspected from the rear. The thickness of the linings  
may not be less than 1 mm (0.04 in).  
min.  
1 mm  
At their most worn point brake pad linings should not be thinner than 1 mm,  
otherwise they could lead to brake failure. For your own safety don’t put off  
having your brake pads changed.  
If the brake pads are replaced too late so that the lining is partly or entirely  
worn, the steel components of the brake pad will rub against the brake disc,  
thereby imparing the braking effect and destroying the brake disc.  
Replacing the rear brake pads (50 SX) *  
Dismount the rear wheel (see "Dismounting the rear wheel").  
Press the brake shoes apart with a suitable screwdriver to allow the brake  
pistons to return to their basic position.  
5
Remove the locking screw [4], unscrew the screw [5] and pull the brake shoes  
out of the brake caliper.  
4
Slide new brake shoes into the brake caliper a fasten with the screw [5].  
Tighten the screw to 10 Nm and mount the locking screw [4].  
Mount the rear wheel and actuate the foot brake lever until you can feel the  
pressure point.  
– It is very important to keep the brake disk free from oil and fatty matters.  
Otherwise, the braking effect would be strongly reduced.  
– After assembly, check if circlips have been fitted correctly.  
– After working on the braking system, one must always actuate the hand  
brake lever or foot brake lever, respectively so as to ensure that the brake  
pads will lie against the brake disk and the pressure point is established.  
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Removing and mounting the front wheel  
Jack the motorcycle up by the frame so that the front wheel is suspended  
above the ground.  
Undo the hexagon nut [1] and remove it together with the washer.  
Hold the front wheel and pull out the wheel spindle [2].  
Carefully take the front wheel out of the fork.  
1
– Do not operate the hand brake when the front wheel has been dismounted.  
– Make sure the brake disc is always on top when you lay down the wheel,  
otherwise the brake disc can be damaged.  
Lift the front wheel into the fork and correctly position it.  
Mount the wheel spindle [2].  
Mount the washer and the hexagon nut [1] and tighten 40 Nm.  
Put the motorcycle back on the ground and operate the front wheel brake until  
the working point is reached.  
– If you don’t happen to have a torque wrench at hand, make sure you have  
the tightening torque corrected by a KTM dealer as soon as possible. A  
loose axle may lead to an unstable driving behavior of your motorcycle.  
– After mounting the front wheel, keep operating the hand brake until the  
pressure point returns.  
2
– It is very important to keep the brake disk free from oil and fatty matters,  
eitherwise the braking effects would be strongly reduced.  
25  
Removing and mounting the rear wheel  
Prop up the motorcycle under the frame.  
Remove hexagon nut [3] on the wheel spindle and disk.  
Hold the rear wheel and remove the wheel spindle.  
Move the rear wheel forwards, remove chain, lift the rear wheel out of the  
swinging fork and remove the brake anchor.  
3
4
– Do not operate the rear brake when the rear wheel has been dismounted.  
– Make sure the brake disc is always on top when you lay down the wheel,  
otherwise the brake disc can be damaged (50 SX).  
To mount the wheel reverse the procedure described above.  
Always hook the brake backing plate into the swing arm support.  
Before tightening the hexagon nut of the wheel spindle, ensure that the  
supporting plates [4] are resting against the swing arm. Additionally, check  
that the rear wheel is aligned with the front wheel.  
4
Tighten the hexagon nut to 40 Nm.  
– If you don’t happen to have a torque wrench at hand, make sure you have  
the tightening torque corrected by a KTM dealer as soon as possible. A  
loose axle may lead to an unstable driving behavior of your motorcycle.  
– After mounting the rear wheel, keep operating the rear brake until the pres-  
sure point returns (50 SX).  
– It is very important to keep the brake disk free from oil and fatty matters,  
otherwise the braking effects would be strongly reduced (50 SX).  
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Tires, air pressure  
Tire type, tire condition, and air pressure level affect the way your motorcycle  
rides, and they must therefore be checked whenever you are getting ready to  
go anywhere on your motorcycle.  
– Tire size can be found in the technical specifications.  
– Tire condition has to be checked every time you want to ride your motor-  
cycle. Before leaving, check tires for punctures and nails or other sharp  
objects that might have become embedded in them.  
– Regularly check the "cold" tire pressure. Correct tire pressure (1.0 bar /  
14 psi) guarantees optimum grip and maximum tire life.  
– Damaged tires must be replaced immediately to protect your youngster.  
– Worn tires can have a negative effect on how the motorcycle performs,  
especially on wet surfaces  
– Tire pressure below the normal level will lead to premature tire wear.  
26  
Checking spoke tension  
The correct spoke tension is very important for the stability of the wheels and  
thus for riding safety. A loose spoke causes the wheel to become  
unbalanced and before long other spokes will have come loose. Check spoke  
tension, especially on a new motorcycle, at regular intervals. If necessary, have  
the spokes retightened and the wheel centered by a KTM dealer.  
– Spokes can tear if you continue to ride with them loose. This may lead to  
an unstable handling of your motorcycle.  
– Excessively tensioned spokes may rupture due to local overloading. The  
spokes must be tensioned to 2.5 - 3 Nm.  
Cooling system  
The water pump [1] in the engine keeps the cooling liquid in circulation.  
The cooling liquid is cooled by the air stream. Therefore, the cooling effect  
is reduced when the traveling speed is reduced. Dirty radiators additionally  
reduce the cooling effect.  
The cooling liquid can be drained by removing screw [2] on the water-pump  
cover.  
1
2
Do not remove any cooler hoses or the drain screw when the engine is hot.  
A mixture of 50 % antifreeze and 50 % distilled water is used as the cooling  
liquid. How-ever, the antifreeze protection must be at least -25° C (-13° F).  
This mixture offers antifreeze protection but also good corrosion protection  
and should therefore not be replaced by pure water.  
3
For the cooling system, use only with high-grade antifreeze (Motorex Anti-Freeze).  
Using lower-grade antifreeze agents can cause corrosion and coolant  
foaming.  
Pressure induced by heating of the coolant in the system is controlled by  
a valve in the radiator cap [3]; a water temperature rising up to 120° C  
(248° F) is admissible without fear of problems.  
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Checking coolant level  
The coolant should be 10 mm (0.4 in) above the radiator fins when the engine  
is cold (see illustr.). In the event of the coolant being drained, always fill and  
bleed the system.  
10 mm  
If possible, always check level of cooling liquid when engine is cold. If you  
have to open the radiator cap when the engine is hot, use a rag to cover the  
cap and open slowly to release pressure.  
when engine is cold  
Cleaning the air filter *  
The air filter must be cleaned at intervals depending on the amount of dust  
accumulated. To clean the air filter, first remove the seat. Then press both  
retaining clips [1], remove the filter holder and the air filter [2]. The air  
filter consists of a foam rubber insert soaked with filter oil.  
1
1
– Do not clean the foam filter with fuel or petroleum since these will dam-  
age the foam. KTM recommends the products (Motorex Liquid Bio Power)  
for air filter maintenance.  
– Never operate your motorcycle without an air filter. Otherwise, dust and  
dirt may get into the engine and lead to increased wear.  
– The holder must retain the air filter throughout its entire circumference.  
If the filter has been mounted incorrectly, the engine will take in unfil-  
tered air, thereby causing increased engine wear.  
27  
2
Thoroughly wash the foam filter in special cleaning fluid (Motorex Bio Dirt  
Remover) and allow it to dry well. Only press out the filter, do not wring it out  
under any circumstances. Oil the dry foam filter with a high-grade filter  
oil ( Motorex Liquid Bio Power). Also clean the air filter box. Check carbure-  
tor collar for damage and that it is filled correctly.  
Insert the air filter in the opening and fasten it with the filter holder. Then  
mount the seat.  
Exhaust system *  
5
6
The silencer is filled with glass-fiber yarn for damping. When in use, the glass-  
fiber yarn becomes loose or coked with oil carbon. This can lead to a power  
loss and a reduction of the silencer damping. The glass-fiber yarn packing  
can be replaced in a few easy steps.  
To replace, remove the silencer from the vehicle and mark the position of the  
outer tube [3] to the inner tube [4]. Remove screws [5] and the end cap [6].  
Pull of the outer tube and remove the old glass-fiber yarn packing [7] from  
the inner tube. Thoroughly clean all parts.  
3
7
To assemble, mount a new glass-fiber yarn packing onto the inner tube (see  
illustration) and slide into the outer tube. Mount end cap and fix with  
screws [5]. Before tightening the screws, turn the outer tube until they match  
the positions you marked. Mount the silencer and check the exhaust system  
for tightness.  
4
Note: Glass fiber yarn packages are offered by your licensed KTM dealer.  
The exhaust system becomes very hot while the motorcycle is running. to avoid  
burns do not start work on the exhaust system until it has properly cooled  
down.  
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Changing the seat height  
The saddle can easily be raised by 25 mm (1 in). This lets you adjust the  
height as your child grows.  
A
B
Figures A and B show the fork and shock absorber positions for a low seat  
position. The fork tubes extend approx. 17 mm (0.7 in) (H) above the upper  
fork stabilizer. The shock absorber is attached to the upper hole in the frame.  
Tighten the clamp screws on the fork stabilizers to 25 Nm (top) and  
10 Nm (bottom), the screw on the shock absorber to 45 Nm.  
H
Figures A and B: low seat position  
Figures C and D: high seat position  
Figures C and D show the fork and shock absorber positions for a high seat  
position.Fork tubes are plane with top of upper fork stabilizer. (Screw cap  
(Aluminium) protrudes from the top of the upper fork stabilizer)  
The shock absorber is attached to the lower hole in the frame. Tighten the  
clamp screws on the fork stabilizers to 25 Nm (top) and 10 Nm (bottom), the  
screw on the shock absorber to 45 Nm.  
C
D
The fork tubes may not be lowered any further than as described above, oth-  
erwise the clamping on the upper fork stabilizer will no longer be adequate.  
28  
Adjusting the throttle cable *  
There must always be a 3 to 5 mm (0.1 to 0.2 in) play in the throttle cable.  
To check this, move back the protective cover [1] on the throttle grip. You  
must be able to lift the outer covering of the cable 3-5 mm from the adjust-  
ing screw [2], until resistance is felt.  
To adjust, loosen the counter nut [3] and turn the adjusting screw accord-  
ingly. Finally tighten counter nut and slide the protective cover back on.  
3-5 mm  
3
2
1
Adjusting the idle speed Dell’Orto PHVA 14 DS (50 SX Junior) *  
The idle speed can be adjusted with screw [4].  
The idle speed is increased by turning clockwise.  
The idle speed is reduced by turning counter-clockwise.  
4
Adjusting the idle speed Dell’Orto PHBG 19 BS (50 SX) *  
The idle speed can be adjusted with screw [5].  
The idle speed is increased by turning clockwise.  
The idle speed is reduced by turning counter-clockwise.  
5
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Checking the gear oil level  
To check the gear oil level, first remove the plug [1]. With the motorcycle parked  
in an upright position, a small quantity of oil should flow out of the indicator  
opening [2]. If oil must be added, tilt the motorcycle and pour automatic gear  
oil (Motorex ATF Super) into the bore.  
1
Less oil or a poor oil quality lead to premature transmission wear. Therefore,  
only use branded products (Motorex ATF Super).  
2
Changing gear oil *  
The engine must be warmed up before changing the gear oil. Park the motor-  
cycle on a horizontal surface, remove the oil drain plug [3] and drain the used  
oil into an appropriate container. Clean the sealing surface, mount the oil drain  
plug together with the gasket and tighten to 15 Nm.  
3
29  
Remove stopper [4] and fill in 0.15 liters of automatic gear oil (Motorex ATF  
Super). Mount the stopper and check the engine for tightness.  
4
Less oil or a poor oil quality lead to premature transmission wear. Therefore,  
only use branded products (Motorex ATF Super).  
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
Adjusting the centrifugal clutch *  
A correctly adjusted centrifugal clutch will provide maximum engine perform-  
ance and ease of driving and prevent the engine from overheating. Clutch wear  
can affect the clutch engagement speed.  
The clutch will slip for a longer period of time at higher clutch engagement  
speeds, generating more frictional heat and causing the engine to overheat.  
If the clutch engagement speed is too low, the engine will not reach the per-  
formance range. In both cases, the engine will not seem to have enough power.  
Check the clutch engagement speed every 20 hours and correct if necessary  
or have it corrected by an authorized KTM workshop.  
1
2
1
1
1
1
1
To tune your clutch, lay the bike on the left side. To prevent oil from leaking  
from the transmission vent hose, run the hose upwards and fasten. Remove  
the screws [1] and the clutch cover [2] and discard the gasket.  
Block the centrifugal clutch [3] with a suitable driver [4].  
4
3
NOTE: insert the driver through both holes in the primary drive's drum and  
gear wheel.  
Loosen the nut [5] on the clutch and pull out the driver.  
Remove the nut and shim from the crankshaft.  
5
30  
Screw the extractor (special tool item no. 590.29.021.044) onto the clutch  
hub [6] with the M5x50 screws, hold the extractor and remove the centrifu-  
gal clutch from the crankshaft by screwing in the extractor screw.  
Completely remove the centrifugal clutch, bearings and spacing washers from  
the crankshaft.  
Loosen the HH screws [7] and remove the clutch shoes [8] from the clutch  
hub [6]. Remove the HH screws and bushings [9], the spring sets [10] and  
the disks [11] from the clutch shoes.  
6
ADJUSTING THE CLUTCH ENGAGEMENT SPEED:  
The spring sets contain 14 spring washers [12] that need to be positioned on  
top of each other in the order shown in the illustration [A].  
Washers are located between the spring sets and the clutch shoes to preten-  
sion the spring sets. You can influence the clutch engagement speed by pre-  
tensioning the spring set. 0.5 mm more pretension will increase the clutch  
engagement speed by approx. 500 rpm.  
8
8
The clutch engagement speed is the speed at which the clutch begins to engage  
and the motorcycle starts to drive off. The clutch engagement speed is 8500-  
9000 rpm for the 50 LC engine.  
6
NOTE: a tachometer (special tool item no. 451.29.075.000) to test the clutch  
engagement speed is available from your KTM dealer.  
8
11  
Make sure the spring sets are not soiled during service or repair work to the  
clutch since this can cause them to malfunction.  
9
10  
7
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MAINTENANCE WORK ON CHASSIS AND ENGINE »  
CORRECTING CLUTCH WEAR:  
10  
Check the clutch shoes for wear. If the surface is only slightly worn you can  
remount them again.  
8
NOTE: The centrifugal clutch has an outer diameter of approx. 82.5 mm  
when new.  
11  
12  
To correct slight wear to the surface, you can insert one of the pretensioning  
disks [11] from each clutch spring between the clutch hub and the clutch  
shoes – see illustration.  
6
If only one disk is installed, you can go ahead and use it.  
The inner diameter of the centrifugal clutch drum may not exceed 84.4 mm  
(new condition 84.0 mm).  
7
Assemble in the reverse order.  
A
Apply Loctite 243 to the HH screws [7] and tighten to 12 Nm.  
Apply Loctite 243 to the M10x1.25 nut [5] on the crankshaft and tighten to 35 Nm.  
Mount a new gasket and position the clutch cover [2].  
Screw on the clutch cover with 6 M6x25 screws [1] and tighten to 10 Nm.  
Move the transmission vent hose back in the original position.  
11  
31  
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TROUBLE SHOOTING »  
If you let the specified maintenance work on your motorcycle be carried out, disturbances can hardly be expected. Should an error  
occur nevertheless, we advise you to use the trouble shooting chart in order to find the cause of error.  
We would like to point out that many operations cannot be performed by oneself. In case of uncertainty, please contact a KTM-dealer.  
TROUBLE  
CAUSE  
REMEDY  
Engine fails to start  
Operating error  
Open fuel tap, replenish fuel, do not use choke  
The motorcycle was not driven for a longer The highly inflammable components in modern fuels volatilize  
period of time, leaving old fuel in the float if left standing for longer periods of time. If the motorcycle  
chamber  
has not been used for over 1 week, the fuel should be drained  
from the float chamber. The engine will start up immediately  
if the float chamber is filled with fresh, ignitable fuel  
Fuel supply interrupted  
Close fuel tap, loosen fuel hose at carburettor, lead into a basin  
and open fuel tap,  
– if fuel leaks out, clean carburettor  
– if no fuel leaks out, check tank ventilation, i.e. clean fuel  
tap  
Electrode distance too large  
Reduce electrode distance (0.60 mm)  
Clean spark plug or renew  
Plug fouled by oil, wet or bridged  
Ignition wire or spark plug connector Dismount spark plug, connect ignition cable, hold to ground  
damaged  
(blank place on engine) and actuate kickstarter, a strong spark  
must be produced at the spark plug  
32  
– If no spark is produced, loosen spark plug cap from igni-  
tion cable, hold about 5 mm from ground and actuate kick-  
starter  
– If a spark now occurs, replace spark plug cap  
– If no spark is produced, control ignition system  
Kill button wire or short-circuit switch Disconnect black coloured cable from short circuit button at  
faulty  
ignition coil and check ignition spark. If the spark is O.K. repair  
defective part of cable or ignition switch  
Loose ignition cable connectors  
Spark too weak  
Inspect cable connectors  
Examine ignition system  
Water in the carburetor and jets blocked Dismantle and clean carbureto  
Engine without idle running Idle adjusting screw out of adjustment Readjust idle running or replace idle adjusting screw  
Ignition system damaged  
Wear  
Examine ignition system  
Overhaul engine  
Less power of engine  
Air filter obstructed  
Clean or renew airfilter  
Fuel supply partly interrupted or blocked Blow through fuel pipe and clean carburetor  
Loss of compression due to loose spark Tighten spark plug  
plug  
Exhaust system damaged  
Check exhaust system for damage  
Check and adjust ignition  
Engine has not enough preignition  
Reed paddles tensionless or damaged, sur- Replace reed paddles or reed valve housing  
face of reed valve housing damaged  
Wear  
Overhaul engine  
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TROUBLE SHOOTING »  
TROUBLE  
CAUSE  
REMEDY  
Engine stalling or running Carburetor overflows if level adjust too high, float Clean carburetor, if necessary replace float needle and  
with four stroke cycle  
needle seating is dirty or enlarged  
adjust level  
Loose carburetor jets  
Tighten jets  
High rpm misfiring  
Incorrect heat range spark plug or  
low quality spark plug  
Refer to technical data section  
Loose, corroded or non conductive ignition socket Check and seal with silicon  
connector  
Engine spluters into the car- Lack of fuel  
buretor  
Clean fuel pipes, examine tank aeration and clean  
Spark plug with incorrect heat value (Ignition by Fit correct spark plug  
incandescence)  
Engine takes air out of control  
Check intake flange and carburettor if firmly setted  
Engine overheating  
Insufficient liquid in cooling system  
Top up coolant and bleed cooling system check cool-  
ing system for leaks  
Radiator fins clogged  
Clean radiatar fins with water jet  
Frothing in cooling system  
Renew coolant using branded anti-freeze/anti-corro-  
sive (Motorex Anti-Freeze)  
The motorcycle is being driven too slowly, the clutch Drive the motorcycle faster or reduce the preload on  
33  
keeps slipping, causing heat to develop  
the clutch springs  
Pinched or kinked water hoses  
Replace with correct routed hoses  
Incorrect ignition timing because of loose stator Readjust to correct ignition timing specifications,  
screws  
secure screws with Loctite 243  
Incorrect compression ratio  
Measure and adjust compression ratio  
Emission of white smoke Cylinder head or O-ring of cylinder head gasket Check cylinder head, replace O-ring  
(steam) leaks  
Excessive oil escapes from Excessive oil quantity in transmission  
transmission breather tube  
Correct transmission oil level  
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CLEANING »  
Clean your motorcycle regularly in order to keep its painted finish looking shiny and new.  
The best manner would be to use warm water that has been mixed with a commercially available washing detergent and a sponge. The  
hard dirt can be removed before with the help of a soft water jet.  
Never clean your motorcycle with a high-pressured cleaner or a high-pressured water jet, otherwise the water might run into the elec-  
trical components, connectors, sheathed cables, bearings, carburetor etc. and cause mailfunctions, i.e., lead to the premature destruc-  
tion of these parts.  
– You should use commercially available detergents to clean the motorcycle. Heavily soiled parts should also be cleaned with the  
help of a paint brush.  
– Before cleaning with water, plug the exhaust pipe to prevent water ingress.  
– After the motorcycle has been rinsed with a soft water jet, it should be dried by air pressure and a cloth. Then take a short drive  
until the engine has reached its operating temperature, and also operate the brakes. The heat also causes the water at the inac-  
cessible parts of the engine and the brakes to evaporate.  
– Slide back the protective covers on the handlebar-mounted instruments so that any water that may have seeped into this part of  
the motorcycle is allowed to evaporate.  
– After the motorcycle has cooled down, oil and grease all the gliding bearing parts. Also treat the chain with a chain spray.  
– To prevent failures in the electric system, you should treat the short circuit button with a contact spray.  
34  
STORAGE »  
If you want to put your motorcycle away for longer periods of time, please observe the following instructions:  
– Clean motorcycle thoroughly (see chapter: CLEANING)  
– Change engine oil (old engine oil contains aggressive contaminations).  
– Check antifreeze and amount of cooling liquid.  
– the engine warm up again, close fuel tap and wait until the engine dies off by itself. In this way, the carburetor jets are prevented  
from becoming resin-clogged by the old fuel.  
– Remove spark plug and fill in approx. 5 cc of engine oil into the cylinder through the opening. Actuate kickstarter 10 times in order  
to distribute the oil onto the cylinder walls and mount the spark plug.  
– Let fuel flow out of tank into an appropriate basin.  
– Correct tire pressure.  
– Lubricate bearing points of the control levers, footrests, etc. as well as the chain.  
– The storage place should be dry and not be subjected to overly great temperature fluctuations.  
– Cover the motorcycle with an air permeable tarpaulin or blanket. Do not use airtight materials, as possible humidity might not be  
able to escape and thereby cause corrosion.  
It would be very bad to let the engine run for a short time during the storage period. The engine would not get warmed up enough and  
the thus developed steam would condense during the combustion process and cause the exhaust to rust.  
USE AFTER PERIOD OF STORAGE  
– Fill up tank with fresh fuel.  
– Check motorcycle as before each start (see driving instructions).  
– Take a short, careful test ride first.  
NOTE: Before you put your motorcycle away for the winter, you should check all parts for their function and wear. Should any service  
jobs, repairs, or any refitting be necessary, you should have them carried out during the off-season (lower workload at mechanics'  
shops). This way, you can avoid the long waiting times at your shop at the beginning of the next biking season.  
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TECHNICAL DATA – ENGINE »  
ENGINE  
50 SX JUNIOR  
50 SX  
Design  
single cylinder 2-stroke engine, with reed valve inlet  
Displacement  
Bore/Stroke  
Fuel  
49.0 cc  
39.5 / 40 mm  
SUPER fuel, research octane no 95, mixed with 2-stroke oil  
Oil/gasoline ratio  
1 : 60 when using high grade 2-stroke oil (Motorex 2T Cross Power) When in doubt,  
please contact your importer  
Lubrication  
mixture lubrication  
Crankshaft bearing  
Connecting rod bearing  
Piston pin bearing  
Piston rings  
2 grooved ball bearing  
needle bearing  
needle bearing  
1 rectangular ring  
Primary drive  
Transmission oil  
Spark plug  
straight cut spur gears, 16 : 57 Z  
0.15-0,2 liter automatic gear oil Dexron II (Motorex Topspeed 4T 15W50)  
NGK BR 8 ECM  
0.6 mm  
Electrode gap  
Carburetor  
Dell’Orto PHVA 14 DS  
Dell’Orto PHBG 19 BS  
Air filter  
wet foam type air filter insert  
Cooling liquid  
0.5 litres, 50% antifreeze, 50% distilled water, at least -25 °C (-13 °F)  
35  
BASIC CARBURETOR SETTING  
Model  
50 SX Junior  
50 SX  
Type  
Dell’Orto PHVA 14 DS  
Dell’Orto PHBG 19 BS  
Main jet  
80  
85  
Needle jet  
211 FA  
45  
260 AU  
48  
Idling jet  
Jet needle  
A10  
3.  
W9  
3.  
Needle position from top  
Air/Mixture reg. screw open  
Slide  
3.5  
40  
3.0  
60  
Starting jet  
60  
60  
TIGHTENING TORQUES - ENGINE  
Primary gear nut  
M14x1,25  
M10x1,25  
M10x1,25  
M7  
40 Nm  
20 Nm  
Hexagon nut ignition rotor  
Nut of clutch hub  
Cylinder head screws  
Cylinder base nuts  
Allan head screw-Stator  
Oil plug  
Loctite 243 + 35 Nm  
15 Nm  
M8  
18 Nm  
M5x25  
M16  
Loctite 243 + 8 Nm  
5 Nm  
Oil drain plug  
M10  
15 Nm  
Other engine screws  
M5  
7 Nm  
M6  
10 Nm  
M8  
30 Nm  
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TECHNICAL SPECIFICATIONS - CHASSIS »  
CHASSIS  
50 SX JUNIOR  
50 SX  
Frame  
single downtube, split-cradle  
Marzocchi Ø = 32 mm  
140/205 mm (5.5/8 in)  
Central shock absorber WP  
Disk brake Ø 160 mm (6.4 in)  
Drum brake Ø 90 mm (3.5 in)  
Pirelli 2.50-10 33J Scorpion  
Pirelli 2.75-10 37J Scorpion  
front/rear: 1.0 bar  
1.8 Liters  
Fork  
Wheel travel front/rear  
Rear suspension  
Front brake  
185/185 mm (7.3/7.3 in)  
Rear brake  
Disk brake Ø 140 mm (5.5 in)  
Pirelli 60/100-12 36NHS Scorpion  
Pirelli 2.75-10 37J Scorpion  
Tires front  
Tires rear  
Tire pressure  
Fuel tank capacity  
Final drive ratio  
Chain  
11 : 48  
10 : 44  
1/2x3/16“ 96 rolls  
66°  
1/2x3/16“ 102 rolls  
Steering angle  
Wheel base  
910 mm (35.8 in)  
585 mm/610 mm (23/24 in)  
220 mm (8.6 in)  
1030 mm (40 in)  
Seat height, unloaded  
Ground clearance  
Rider’s body height  
Rider’s body weight  
Recommended age of rider  
Engine  
650/675 mm (25.6/26.6 in)  
255 mm (10 in)  
max. 130 cm (51 in)  
max. 35 kg (78 lbs)  
4-7 years  
6-10 years  
36  
50 LC  
TIGHTENING TORQUES  
Hexagon nuts front/rear axle  
Hexagon nut swing arm bolt  
Clamping screw upper fork bridge  
Clamping screw lower fork bridge  
Screws handlebar clamp  
Shock absorber top/bottom  
Allan screw – Handlebar support  
Front brake caliper  
M12x1  
40 Nm  
45 Nm  
M10  
M8  
25 Nm  
M6  
10 Nm  
M8  
20 Nm  
M10  
M10  
M8  
45 Nm  
Loctite 243 + 40 Nm  
Loctite 243 + 20 Nm  
Loctite 243 + 15 Nm  
3 Nm  
Front/rear brake disk  
M6  
Spoke nipple  
M4  
Other chassis screws  
M5  
6 Nm  
M6  
10 Nm  
M8  
25 Nm  
M10  
45 Nm  
STANDARD-ADJUSTMENT – FORK  
Spring  
2,0 N/mm  
Preload  
10 mm (0.4 in)  
SAE 7,5  
Fork oil  
Air chamber length  
110 mm (4.3 in)  
STANDARD ADJUSTMENT - SHOCK ABSORBER  
50 SX Junior  
50 SX  
WP 03189D01  
WP 03189D02  
Rebound adjuster  
Spring  
12  
10  
75 N/mm  
5 mm (0.2 in)  
35 N/mm  
3 mm (0.12 in)  
Spring preload  
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HEAD WORD INDEX »  
Page  
Filler cap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7  
Foot brake lever . . . . . . . . . . . . . . . . . . . . . . . . . . . .8  
Fuel tap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7  
General information about KTM disc brakes . . . . . . .21  
General Tips and Warnings for starting the motorcycle . .10  
Hand brake lever . . . . . . . . . . . . . . . . . . . . . . . . . . .7  
How to change the handlebar position . . . . . . . . . . .17  
Important Information for parents about safe driving . . .4  
Instructions for the first ride . . . . . . . . . . . . . . . . . .10  
Kickstarter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8  
Maintenance work on chassis and engine . . . . . . . . . .16  
Operation instruments . . . . . . . . . . . . . . . . . . . . . . . .7  
Periodic maintenance schedule . . . . . . . . . . . . . . . .14  
Plugin - Stand (50 SX) . . . . . . . . . . . . . . . . . . . . . . .9  
Rebound damping function of the shock absorber . . . .9  
Refilling the rear brake fluid reservoir (50 SX) . . . . . .24  
Refueling, fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . .13  
Removing and mounting the front wheel . . . . . . . . . .25  
Removing and mounting the rear wheel . . . . . . . . . .25  
Removing the seat . . . . . . . . . . . . . . . . . . . . . . . . .16  
Replacing the front brake pads . . . . . . . . . . . . . . . .22  
Replacing the rear brake pads (50 SX) . . . . . . . . . . . .24  
Running in . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10  
Serial number locations . . . . . . . . . . . . . . . . . . . . . . .6  
Setting the basic position and play of the hand brake lever . .21  
Short circuit button . . . . . . . . . . . . . . . . . . . . . . . . .6  
Side stand . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8  
Starting off . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12  
Starting when the engine is cold . . . . . . . . . . . . . . .12  
Starting when the engine is warm . . . . . . . . . . . . . .12  
Stopping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13  
Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34  
Technical data – engine . . . . . . . . . . . . . . . . . . . . . .35  
Technical specifications - chassis . . . . . . . . . . . . . . .36  
Telescopic fork maintenance . . . . . . . . . . . . . . . . . .19  
Throttle grip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6  
Tires, air pressure . . . . . . . . . . . . . . . . . . . . . . . . . .26  
To determine the sag of the shock absorber . . . . . . . .18  
To determine the sag of the telescopic fork . . . . . . .18  
Trouble shooting . . . . . . . . . . . . . . . . . . . . . . . . . . .32  
What to do when the engine is “flooded” . . . . . . . . .12  
What you should check before each start . . . . . . . . .11  
Page  
Adjusting the centrifugal clutch . . . . . . . . . . . . . . . . . .30  
Adjusting the control cable on the rear wheel (50 SX Junior) .23  
Adjusting the idle speed (Dell’Orto PHBG 19 BS) . . .28  
Adjusting the idle speed (Dell’Orto PHVA 14 DS) . . .28  
Adjusting the throttle cable . . . . . . . . . . . . . . . . . . .28  
Basic suspension setup for the weight of the driver . .18  
Braking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13  
Chain maintenance . . . . . . . . . . . . . . . . . . . . . . . . .20  
Changing gear oil . . . . . . . . . . . . . . . . . . . . . . . . . .29  
Changing spring preloading of the shock absorber . . .20  
Changing the basic position of the foot brake lever  
(50 SX Junior) . . . . . . . . . . . . . . . . . . . . . . . . . . . .23  
Changing the basic position of the foot brake lever (50 SX) . .23  
Changing the seat height . . . . . . . . . . . . . . . . . . . . .28  
Changing the telescopic fork oil . . . . . . . . . . . . . . . .19  
Chassis number . . . . . . . . . . . . . . . . . . . . . . . . . . . .6  
Check chain tension . . . . . . . . . . . . . . . . . . . . . . . .20  
Checking and adjusting the steering head bearing  
37  
(50 SX Junior) . . . . . . . . . . . . . . . . . . . . . . . . . . . .16  
Checking and adjusting the steering head bearing  
(50 SX) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17  
Checking coolant level . . . . . . . . . . . . . . . . . . . . . .27  
Checking front brake pads . . . . . . . . . . . . . . . . . . . .22  
Checking rear brake pads (50 SX) . . . . . . . . . . . . . .24  
Checking spoke tension . . . . . . . . . . . . . . . . . . . . .26  
Checking the brake fluid level/ refilling . . . . . . . . . . .22  
Checking the gear oil level . . . . . . . . . . . . . . . . . . .29  
Checking the rear brake fluid level (50 SX) . . . . . . . .23  
Checking the rear brake linings for wear  
(50 SX Junior) . . . . . . . . . . . . . . . . . . . . . . . . . . . .23  
Choke (Dell’Orto carburetor PHBG 19 BS) . . . . . . . . .8  
Choke (Dell’Orto carburetor PHVA 14 DS) . . . . . . . . . .8  
Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34  
Cleaning the air filter . . . . . . . . . . . . . . . . . . . . . . .27  
Cleaning the dust scrabbers of the telescopic fork . . .20  
Cooling system . . . . . . . . . . . . . . . . . . . . . . . . . . . .26  
Correct chain tension . . . . . . . . . . . . . . . . . . . . . . .20  
Driving . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12  
Driving instructions . . . . . . . . . . . . . . . . . . . . . . . . .11  
Drum brake maintenance (50 SX Junior) . . . . . . . . .23  
Engine number . . . . . . . . . . . . . . . . . . . . . . . . . . . .6  
Exhaust system . . . . . . . . . . . . . . . . . . . . . . . . . . .27  
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38  
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39  
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40  
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