KTM 125 SX 2021 Owner's Manual
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KTM 125 SX 2021 Owner's Manual

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OWNER'S MANUAL
2021
125 SX
150 SX
125 XC
Art. no. 3214209en

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Table of Contents
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Summary of Contents for KTM 125 SX 2021

  • Page 1 OWNER'S MANUAL 2021 125 SX 150 SX 125 XC Art. no. 3214209en...
  • Page 3 KTM accepts no liability for delivery options, deviations from fig- ures and descriptions, misprints, and other errors. The models portrayed partly contain special equipment that does not belong to the regular scope of supply.

  • Page 4: Table Of Contents

    TABLE OF CONTENTS PREPARING FOR USE......... 22 TABLE OF CONTENTS MEANS OF REPRESENTATION ...... 5 Advice on preparing for first use ..22 Symbols used ........5 Running in the engine ...... 23 Formats used........5 Starting power of lithium-ion SAFETY ADVICE..........
  • Page 5 TABLE OF CONTENTS 10.10 Adjusting the spring preload of the 11.33 Checking the chain for dirt....69 shock absorber ......43 11.34 Cleaning the chain ......70 10.11 Adjusting the riding sag ....44 11.35 Checking the chain tension ....70 10.12 Checking the basic setting of the 11.36 Adjusting the chain tension....
  • Page 6 TABLE OF CONTENTS 15 COOLING SYSTEM ........102 21.3.5 Carburetor tuning (150 SX)..131 21.3.6 Basic carburetor setting for 15.1 Cooling system ......102 sandy surfaces (150 SX)..... 132 15.2 Radiator cover ....... 102 21.3.7 125 XC US ....... 133 15.3 Installing the radiator cover.....

  • Page 7: Means Of Representation 1

    All work marked with this symbol requires specialist knowledge and technical understanding. In the interest of your own safety, have these jobs performed by an authorized KTM workshop! Your motorcycle will be optimally cared for there by specially trained experts using the auxiliary tools required.

  • Page 8: Safety Advice

    2 SAFETY ADVICE Use definition – intended use (All SX models) This vehicle has been designed and built to withstand the normal stresses and strains of racing. This vehicle complies with the currently valid regulations and categories of the top international motorsports organizations. Info Only operate this vehicle in closed-off areas remote from public road traffic.

  • Page 9: Degrees Of Risk And Symbols

    SAFETY ADVICE 2 Degrees of risk and symbols Danger Identifies a danger that will immediately and invariably lead to fatal or serious permanent injury if the appropriate measures are not taken. Warning Identifies a danger that is likely to lead to fatal or serious injury if the appropriate measures are not taken.

  • Page 10: Protective Clothing

    – Always wear protective clothing that is in good condition and meets the legal regulations. In the interest of your own safety, KTM recommends that you only operate the vehicle while wearing protective clothing. Work rules Unless specified otherwise, the ignition must be turned off during all work (models with ignition lock, models with remote key) or the engine must be at a standstill (models without ignition lock or remote key).

  • Page 11: Owner's Manual

    The Owner's Manual is an important component of the vehicle and must be handed over to the new owner if the vehicle is sold. The Owner's Manual is also available for download from your authorized KTM dealer and on the KTM website. International KTM Website: http://www.ktm.com...

  • Page 12: Important Notes

    Manufacturer warranty, implied warranty The work prescribed in the service schedule must only be carried out in an authorized KTM workshop and con- firmed in the KTM Dealer.net, as otherwise all warranty claims will be void. Damage or secondary damage caused by tampering with and/or conversions on the vehicle are not covered by the manufacturer warranty.

  • Page 13: View Of Vehicle 4

    VIEW OF VEHICLE 4 View of vehicle, front left (example) S04251-10 Hand brake lever ( p. 15) Clutch lever ( p. 15) Air filter box cover Plug-in stand ( p. 20) (All SX models) Shift lever ( p. 19) Choke ( p.

  • Page 14: View Of Vehicle, Rear Right (Example)

    4 VIEW OF VEHICLE View of vehicle, rear right (example) S04252-10 Seat Fuel tank filler cap Switch-off button ( p. 15) Throttle grip ( p. 15) Kick starter lever ( p. 20) Foot brake lever ( p. 20) Shock absorber compression adjustment Shock absorber rebound adjustment Level viewer for brake fluid, rear...

  • Page 15: Serial Numbers 5

    SERIAL NUMBERS 5 Vehicle identification number The vehicle identification number is stamped on the right side of the steering head. 401945-10 Type label The type label is fixed to the front of the steering head. 401946-10 Engine number The engine number is stamped on the left side of the engine under the engine sprocket.

  • Page 16: Shock Absorber Article Number

    5 SERIAL NUMBERS Shock absorber article number Shock absorber article number is stamped on the top of the shock absorber above the adjusting ring towards the engine side. 401948-10...

  • Page 17: Controls 6

    CONTROLS 6 Clutch lever Clutch lever is fitted on the handlebar on the left. The clutch is activated hydraulically and adjusts itself automati- cally. F00009-10 Hand brake lever Hand brake lever is fitted on the right side of the handlebar. The front brake is engaged using the hand brake lever.

  • Page 18: Start Button (125 Xc Us)

    6 CONTROLS Start button (125 XC US) Start button is fitted on the right side of the handlebar. Possible states • The start button is in the basic position is pressed – In this position, the starter • The start button motor is actuated.

  • Page 19: Closing The Fuel Tank Filler Cap

    CONTROLS 6 (All SX models) – Turn fuel tank filler cap counterclockwise and lift it off. K01132-11 (125 XC US) – Press release button , turn the fuel tank filler cap coun- terclockwise, and lift it off. K01334-10 Closing the fuel tank filler cap (All SX models) –...

  • Page 20: Fuel Tap (All Sx Models)

    6 CONTROLS Fuel tap (All SX models) The fuel tap is on the left side of the fuel tank. Open or close the fuel supply to the carburetor using tap han- on the fuel tap. Possible states Fuel supply closed OFF – Fuel cannot flow from the fuel tank •...

  • Page 21: Choke

    CONTROLS 6 6.11 Choke (All SX models) Choke is fitted on the left side of the carburetor. K01129-10 (125 XC US) Choke is fitted on the left side of the carburetor. Activating the choke function frees a drill hole in the carburetor through which the engine can draw extra fuel.

  • Page 22: Kick Starter Lever

    6 CONTROLS 6.13 Kick starter lever Kick starter lever is fitted on the right side of the engine. The kick starter lever can be swiveled. Info Before riding, swing the kick starter lever inwards towards the engine. 401954-10 6.14 Foot brake lever Foot brake lever is located in front of the right footrest.
  • Page 23 CONTROLS 6 The side stand is used for parking the motorcycle. Info When you are riding, side stand must be folded up and secured with rubber strap 401944-10...

  • Page 24: Preparing For Use

    When using your motorcycle, remember that others may feel disturbed by excessive noise. – Make sure that the pre-sales inspection work has been carried out by an authorized KTM workshop. You will receive a delivery certificate when the vehicle is handed over.

  • Page 25: Running In The Engine

    PREPARING FOR USE 7 – Adjust the basic position of the foot brake lever. p. 86) – Adjust the basic position of the shift lever. p. 115) – Get used to the handling characteristics of the motorcycle on a suitable surface before undertaking more chal- lenging trips.

  • Page 26: Preparing The Vehicle For Difficult Operating Conditions

    7 PREPARING FOR USE Preparing the vehicle for difficult operating conditions Info Use of the vehicle under difficult conditions, such as on sand or on wet and muddy circuits/surfaces, can lead to considerably more rapid wear of components such as the drive train, brake system, or suspension components.
  • Page 27 PREPARING FOR USE 7 – Mount the air filter dust cover. Air filter dust cover (79006920000) Info Observe the fitting instructions for KTM PowerParts. M01104-01 – Mount the air filter sand cover. Air filter sand cover (79006922000) Info Observe the fitting instructions for KTM PowerParts.

  • Page 28: Preparing The Vehicle For Riding On Wet Sand

    Change the radiator cap. – Mount the air filter rain cover. Air filter rain cover (79006921000) Info Observe the fitting instructions for KTM PowerParts. M01106-01 – Adjust the carburetor jetting and setting. Info Your authorized KTM workshop can recommend the right carburetor tuning.

  • Page 29: Preparing The Vehicle For Riding On Wet And Muddy Circuits

    Preparing the vehicle for riding on wet and muddy circuits – Mount the air filter rain cover. Air filter rain cover (79006921000) Info Observe the fitting instructions for KTM PowerParts. M01106-01 – Adjust the carburetor jetting and setting. Info Your authorized KTM workshop can recommend the right carburetor tuning.

  • Page 30: Preparing Vehicle For High Temperatures Or Slow Riding

    Straighten the bent radiator fins carefully. – Check the coolant level. ( p. 104) Preparing the vehicle for low temperatures or snow – Mount the air filter rain cover. Air filter rain cover (79006921000) Info Observe the fitting instructions for KTM PowerParts. M01106-01...
  • Page 31 PREPARING FOR USE 7 – Adjust the carburetor jetting and setting. Info Your authorized KTM workshop can recommend the right carburetor tuning. M01107-01...

  • Page 32: Riding Instructions

    8 RIDING INSTRUCTIONS Checks and maintenance measures when preparing for use Info Before every trip, check the condition of the vehicle and ensure that it is safe to operate. The vehicle must be in perfect technical condition when it is being operated. –...

  • Page 33: Starting Off

    RIDING INSTRUCTIONS 8 Info If the motorcycle is unwilling to start, the cause can be old fuel in the float chamber. The flammable ele- ments of the fuel evaporate after a long time of standing. If the float chamber is filled with fresh fuel, the engine starts immediately. The motorcycle has been out of use for more than 1 week –...

  • Page 34: Shifting, Riding

    Danger of accidents A spongy pressure point on the front or rear brake reduces braking efficiency. – Check the brake system and do not continue riding until the problem is eliminated. (Your authorized KTM workshop will be glad to help.) Warning Danger of accidents Moisture and dirt impair the brake system.

  • Page 35: Stopping, Parking

    RIDING INSTRUCTIONS 8 – Use the braking effect of the engine on long downhill stretches. Change down one or two gears, but do not over-rev the engine. You will have to apply the brakes far less frequently as a result and the brake system will not overheat.

  • Page 36: Refueling

    8 RIDING INSTRUCTIONS (All SX models) – Switch off the engine. – Mount plug-in stand on the fork legs. Plug-in stand (79029094000) Info The plug-in stand is included. Make sure the brake line runs in front of the plug-in stand and does not become wedged. H02628-01 –...
  • Page 37 RIDING INSTRUCTIONS 8 – Fill the fuel tank with fuel up to measurement Guideline 35 mm (1.38 in) Measurement of Total fuel tank 7.5 l Super unleaded capacity, approx. (All (1.98 US gal) (98 octane) mixed SX models) with 2-stroke engine oil (1:40) p.

  • Page 38: Service Schedule

    Different service intervals may apply in your country, depending on the local operating conditions. Individual service intervals and scopes may change in the course of technical developments. The most up-to-date service schedule can always be found on KTM Dealer.net. Your authorized KTM dealer will be happy to advise you.

  • Page 39: Recommended Work

    ● Final check: Check the vehicle for operating safety and take a test ride. ○ ● ● ● ● Make a service entry in the KTM Dealer.net. ○ One-time interval ● Periodic interval Recommended work after every race Every 40 operating hours...

  • Page 40: 10 Tuning The Chassis

    – As delivered, KTM offroad motorcycles are adjusted for an average rider's weight (with full protective clothing). Guideline Standard rider weight 75 …...

  • Page 41: Compression Damping Of The Shock Absorber

    The shock absorber is filled with highly compressed nitrogen. – Please follow the description provided. (Your authorized KTM workshop will be glad to help.) Info The effect of the low-speed compression adjuster can be seen in slow to normal compression of the shock absorber.

  • Page 42: Adjusting The High-Speed Compression Damping Of The Shock Absorber

    The shock absorber is filled with highly compressed nitrogen. – Please follow the description provided. (Your authorized KTM workshop will be glad to help.) Info The effect of the high-speed compression adjuster can be seen in fast compression of the shock absorber.

  • Page 43: Measuring The Rear Wheel Dimension Unloaded

    TUNING THE CHASSIS 10 – Turn adjusting screw clockwise up to the last perceptible click. – Turn counterclockwise by the number of clicks corresponding to the shock absorber type. Guideline Rebound damping (All SX models) Comfort 17 clicks Standard 15 clicks K01131-10 Sport 13 clicks...

  • Page 44: Checking The Static Sag Of The Shock Absorber

    10 TUNING THE CHASSIS 10.8 Checking the static sag of the shock absorber – Measure dimension of rear wheel unloaded. ( p. 41) – Hold the motorcycle upright with aid of an assistant. – Measure the distance again between the rear axle and mark- ing SAG on the rear fender using the sag gage.

  • Page 45: Adjusting The Spring Preload Of The Shock Absorber

    The shock absorber is filled with highly compressed nitrogen. – Please follow the description provided. (Your authorized KTM workshop will be glad to help.) Info Before changing the spring preload, make a note of the present setting, e.g., by measuring the spring length.

  • Page 46: Adjusting The Riding Sag

    10 TUNING THE CHASSIS 10.11 Adjusting the riding sag Preparatory work – Raise the motorcycle with a lift stand. ( p. 49) – Remove the shock absorber. p. 58) – After removing the shock absorber, clean it thoroughly. Main work –...

  • Page 47: Adjusting The Fork Air Pressure

    A little air escapes from the fork leg when connecting. Info This is due to the volume of the hose and not due to a defect in the fork airpump or the fork. Read the accompanying KTM PowerParts instructions. – Adjust the air pressure as specified. Guideline Air pressure (All SX models) 8.3 bar (120 psi)

  • Page 48: Adjusting The Compression Damping Of The Fork

    10 TUNING THE CHASSIS When disconnecting, excess pressure will escape from the hose – the fork leg itself does not lose any air. The fork airpump indicator switches off automatically after 80 seconds. – Mount the protection cap. Info Only mount the protection cap by hand. Finishing work –...

  • Page 49: Handlebar Position

    TUNING THE CHASSIS 10 – Take off protection cap – Turn adjusting screw clockwise all the way. Info Adjusting screw is located at the lower end of the right fork leg. – Turn counterclockwise by the number of clicks corresponding to the fork type.
  • Page 50 10 TUNING THE CHASSIS Main work – Remove screws . Remove the handlebar clamp. Remove the handlebar and lay it to one side. Info Cover the components to protect them against damage. Do not kink the cables and lines. – Remove screws .

  • Page 51: Service Work On The Chassis 11

    SERVICE WORK ON THE CHASSIS 11 11.1 Raising the motorcycle with a lift stand Note Material damage The vehicle may be damaged by incorrect procedure when parking. Significant damage may be caused if the vehicle rolls away or falls over. The components for parking the vehicle are designed only for the weight of the vehicle. –...

  • Page 52: Bleeding The Fork Legs

    11 SERVICE WORK ON THE CHASSIS 11.3 Bleeding the fork legs Preparatory work – Raise the motorcycle with a lift stand. ( p. 49) Main work – Release bleeder screws Any excess pressure escapes from the interior of the fork. –...

  • Page 53: Removing The Fork Legs

    SERVICE WORK ON THE CHASSIS 11 11.5 Removing the fork legs Preparatory work – Raise the motorcycle with a lift stand. ( p. 49) – Remove the front wheel. p. 92) Main work – Remove screws and take off the clamp. –...

  • Page 54: Removing The Fork Protector

    11 SERVICE WORK ON THE CHASSIS – Position the brake caliper. Mount and tighten screws Guideline Screw, front 25 Nm (18.4 lbf ft) Loctite ® 243™ brake caliper – Position the brake line and the clamp. Mount and tighten screws K01143-11 Finishing work –...

  • Page 55: Installing The Lower Triple Clamp

    SERVICE WORK ON THE CHASSIS 11 Main work – Remove screw – Remove screw – Take off the upper triple clamp with the handlebar and hang them to the side. Info Cover the components to protect them against damage. Do not kink the cables and lines. K01149-10 –...
  • Page 56 11 SERVICE WORK ON THE CHASSIS – Position the fork legs. Air bleeder screw of the right fork leg is positioned to the front. Valve of the left fork leg faces the front. Info The air suspension AER valve is located in the left fork leg.

  • Page 57: Checking Steering Head Bearing Play

    Danger of accidents Incorrect steering head bearing play impairs the handling characteristic and dam- ages components. – Correct incorrect steering head bearing play immediately. (Your authorized KTM workshop will be glad to help.) Info If the vehicle is operated for a lengthy period with play in the steering head bearing, the bearings and the bearing seats in the frame can become damaged over time.

  • Page 58: Adjusting Steering Head Bearing Play

    11 SERVICE WORK ON THE CHASSIS Finishing work – Remove the motorcycle from the lift stand. ( p. 49) 11.12 Adjusting steering head bearing play Preparatory work – Raise the motorcycle with a lift stand. ( p. 49) – Remove the handlebar cushion. Main work –...

  • Page 59: Removing The Start Number Plate

    SERVICE WORK ON THE CHASSIS 11 11.14 Removing the start number plate – Remove screw – Disconnect the brake line at the start number plate. Take off the start number plate. F00012-10 11.15 Installing the start number plate – Connect the brake line at the start number plate. –...

  • Page 60: Removing The Shock Absorber

    11 SERVICE WORK ON THE CHASSIS 11.18 Removing the shock absorber Preparatory work – Raise the motorcycle with a lift stand. ( p. 49) Main work – Remove the cable ties. – Remove screws with the washers. – Remove screw –...

  • Page 61: Installing The Shock Absorber

    SERVICE WORK ON THE CHASSIS 11 – Remove nut and pull out the fork pivot. – Push the link fork back and secure it against falling over. V01526-10 – Hold the shock absorber and remove screw K01139-10 – Remove the shock absorber carefully at the bottom. K01140-10 11.19 Installing the shock absorber...
  • Page 62 11 SERVICE WORK ON THE CHASSIS – Position link fork and mount fork pivot. Info Pay attention to flat area – Mount and tighten nut Guideline Nut, fork pivot M16x1.5 100 Nm (73.8 lbf ft) V01527-10 – Mount the chain. –...

  • Page 63: Removing The Seat

    SERVICE WORK ON THE CHASSIS 11 – Position left frame protector. – Insert right frame protector from below and push to the rear. – Mount and tighten screws with the washers. Guideline Screw, frame protec- 3 Nm (2.2 lbf ft) –...

  • Page 64: Removing The Air Filter Box Cover

    11 SERVICE WORK ON THE CHASSIS – Mount and tighten screw Guideline Remaining screws, 10 Nm (7.4 lbf ft) chassis K01133-10 11.22 Removing the air filter box cover Condition The air filter box cover is secured. – Remove the seat. ( p.

  • Page 65: Installing The Air Filter Box Cover

    SERVICE WORK ON THE CHASSIS 11 11.23 Installing the air filter box cover Condition The air filter box cover is secured. – Insert the air filter box cover in area and clip it into area K01154-11 – Mount and tighten screw Guideline Screw, air filter box EJOT PT...

  • Page 66: Cleaning The Air Filter And Air Filter Box

    11 SERVICE WORK ON THE CHASSIS Main work – Detach retaining tab . Remove air filter with air filter sup- port. – Take off air filter from air filter support. K01156-10 11.25 Cleaning the air filter and air filter box Note Environmental hazard Hazardous substances cause environmental damage.

  • Page 67: Installing The Air Filter

    SERVICE WORK ON THE CHASSIS 11 11.26 Installing the air filter Main work – Mount the clean air filter on the air filter support. – Grease the air filter in area Long-life grease ( p. 143) 102178-10 – Insert the air filter and position the top retaining pin bushing The air filter is correctly positioned.

  • Page 68: Installing The Main Silencer

    11 SERVICE WORK ON THE CHASSIS – Remove screws with the washers. – Pull off the main silencer from the manifold at exhaust sleeve K01187-10 11.29 Installing the main silencer – Position the main silencer in exhaust sleeve – Mount and tighten screws with the washers.

  • Page 69: Removing The Fuel Tank

    SERVICE WORK ON THE CHASSIS 11 Main work – Remove screws . Pull out inner tube – Remove the glass fiber yarn filling from the inner tube. – Clean the parts that need to be reinstalled and check for dam- age.

  • Page 70: Installing The Fuel Tank

    11 SERVICE WORK ON THE CHASSIS Main work – Pull off the fuel hose. Info Remaining fuel may flow out of the fuel hose. – Remove screws K01189-10 – Remove screw with the rubber bushing. – Pull the fuel tank breather hose off the fuel tank lid. K01190-10 –...

  • Page 71: Checking The Chain For Dirt

    SERVICE WORK ON THE CHASSIS 11 Main work – Check throttle cable routing. ( p. 75) – Position the fuel tank and fit the two spoilers laterally to the radiator. – Make sure that no cables or throttle cables are trapped or dam- aged.

  • Page 72: Cleaning The Chain

    11 SERVICE WORK ON THE CHASSIS 11.34 Cleaning the chain Warning Danger of accidents Lubricants on the tires reduces the road grip. – Remove lubricants from the tires using a suitable cleaning agent. Warning Danger of accidents Oil or grease on the brake discs reduces the braking effect. –...

  • Page 73: Adjusting The Chain Tension

    SERVICE WORK ON THE CHASSIS 11 Main work – Pull the chain at the end of the chain sliding piece upward to measure chain tension Guideline Lower chain section must be taut. Info Chain wear is not always even, so you should repeat this measurement at different chain positions.

  • Page 74: Checking The Chain, Rear Sprocket, Engine Sprocket, And Chain Guide

    11 SERVICE WORK ON THE CHASSIS Main work – Loosen nut – Loosen nuts – Adjust the chain tension by turning adjusting screws left and right. Guideline Chain tension 55 … 58 mm (2.17 … 2.28 in) Turn adjusting screws on the left and right so that the markings on the left and right chain adjusters are in the same position relative to reference marks...
  • Page 75 SERVICE WORK ON THE CHASSIS 11 – Pull on the top section of the chain with the specified weight Guideline Weight, chain wear measure- 10 … 15 kg (22 … 33 lb.) ment – Measure distance of 18 chain rollers in the lower chain section.
  • Page 76 11 SERVICE WORK ON THE CHASSIS – Check the chain sliding piece for wear. » If the lower edge of the chain pins is in line with or below the chain sliding piece: – Change the chain sliding piece. – Check that the chain sliding piece is firmly seated.

  • Page 77: Checking The Frame

    If the link fork exhibits damage, cracking, or deformation: – Change the link fork. Info Always replace a damaged link fork. Repairing the link fork is not authorized by KTM. S02305-01 11.40 Checking throttle cable routing Warning Danger of accidents The throttle cable may slip out of the guide if routed incorrectly.

  • Page 78: Checking The Rubber Grip

    11 SERVICE WORK ON THE CHASSIS Main work – Check throttle cable routing. The throttle cable must be routed along the back of the handlebar, to the right of the frame, above the fuel tank bracket, and to the carburetor. The throttle cable must be secured on the fuel tank bracket with a rubber strap.

  • Page 79: Adjusting The Basic Position Of The Clutch Lever

    SERVICE WORK ON THE CHASSIS 11 11.42 Adjusting the basic position of the clutch lever – Adjust the basic position of the clutch lever to your hand size by turning adjusting screw Info Turn the adjusting screw counterclockwise to decrease the distance between the clutch lever and the handle- bar.

  • Page 80: Changing The Hydraulic Clutch Fluid

    11 SERVICE WORK ON THE CHASSIS Info Clean up overflowed or spilled brake fluid immediately with water. 11.44 Changing the hydraulic clutch fluid Warning Skin irritation Brake fluid causes skin irritation. – Keep brake fluid out of the reach of children. –...
  • Page 81 SERVICE WORK ON THE CHASSIS 11 – Now inject the liquid into the system until it emerges from the drill hole of the master cylinder without bubbles. – Now and then, extract fluid from the master cylinder reservoir to prevent overflow. –...

  • Page 82: 12 Brake System

    Do not make any adjustments while riding. 12.3 Checking the brake discs Warning Danger of accidents Worn-out brake discs reduce the braking effect. – Make sure that worn-out brake discs are replaced immediately. (Your authorized KTM workshop will be glad to help.)

  • Page 83: Checking The Front Brake Fluid Level

    Danger of accidents Old brake fluid reduces the braking effect. – Make sure that brake fluid for the front and rear brake is changed in accordance with the service schedule. (Your authorized KTM workshop will be glad to help.) Preparatory work –...

  • Page 84: Adding Front Brake Fluid

    Danger of accidents Old brake fluid reduces the braking effect. – Make sure that brake fluid for the front and rear brake is changed in accordance with the service schedule. (Your authorized KTM workshop will be glad to help.) Note Environmental hazard Hazardous substances cause environmental damage.

  • Page 85: Checking The Front Brake Linings

    Checking the front brake linings Warning Danger of accidents Worn-out brake linings reduce the braking effect. – Ensure that worn-out brake linings are replaced immediately. (Your authorized KTM workshop will be glad to help.) – Check the brake linings for minimum thickness ≥...
  • Page 86 Danger of accidents Brake linings which have not been approved alter the braking efficiency. Not all brake linings are tested and approved for KTM motorcycles. The structure and friction coefficient of the brake linings, and thus their brake power, may vary greatly from that of original brake linings.
  • Page 87 BRAKE SYSTEM 12 Info Make sure that you do not press the brake caliper against the spokes when pushing back the brake pistons. – Remove cotter pins , pull out pin , and remove the brake linings. – Clean the brake caliper and brake caliper bracket. 101737-10 –...

  • Page 88: Checking The Free Travel Of Foot Brake Lever

    12 BRAKE SYSTEM 12.8 Checking the free travel of foot brake lever Warning Danger of accidents The brake system fails in the event of overheating. If there is no free travel on the foot brake lever, pressure builds up in the brake system on the rear brake.

  • Page 89: Checking The Rear Brake Fluid Level

    Danger of accidents Old brake fluid reduces the braking effect. – Make sure that brake fluid for the front and rear brake is changed in accordance with the service schedule. (Your authorized KTM workshop will be glad to help.) Preparatory work –...
  • Page 90 Danger of accidents Old brake fluid reduces the braking effect. – Make sure that brake fluid for the front and rear brake is changed in accordance with the service schedule. (Your authorized KTM workshop will be glad to help.) Note Environmental hazard Hazardous substances cause environmental damage.

  • Page 91: Checking The Brake Linings Of The Rear Brake

    Checking the brake linings of the rear brake Warning Danger of accidents Worn-out brake linings reduce the braking effect. – Ensure that worn-out brake linings are replaced immediately. (Your authorized KTM workshop will be glad to help.) – Check the brake linings for minimum thickness ≥...
  • Page 92 12 BRAKE SYSTEM Info Never use DOT 5 brake fluid. It is silicone-based and purple in color. Oil seals and brake lines are not designed for DOT 5 brake fluid. Avoid contact between brake fluid and painted parts. Brake fluid attacks paint. Only use clean brake fluid from a sealed container.
  • Page 93 BRAKE SYSTEM 12 – Add brake fluid to level Brake fluid DOT 4 / DOT 5.1 ( p. 141) – Mount and tighten screw cap with membrane and the O-ring. Info Clean up overflowed or spilled brake fluid immediately with water. K01185-10...

  • Page 94: 13 Wheels, Tires

    13 WHEELS, TIRES 13.1 Removing the front wheel Preparatory work – Raise the motorcycle with a lift stand. ( p. 49) Main work – Manually press the brake caliper toward the brake disc to push back the brake pistons. Info Make sure that you do not press the brake caliper against the spokes when pushing back the brake pistons.

  • Page 95: Installing The Front Wheel

    WHEELS, TIRES 13 13.2 Installing the front wheel Warning Danger of accidents Oil or grease on the brake discs reduces the braking effect. – Always keep the brake discs free of oil and grease. – Clean the brake discs with brake cleaner when necessary. –...

  • Page 96: Installing The Rear Wheel

    13 WHEELS, TIRES Main work – Manually press the brake caliper toward the brake disc to push back the brake piston. Info Make sure that you do not press the brake caliper against the spokes when pushing back the brake piston. –...
  • Page 97 WHEELS, TIRES 13 Main work – Check the wheel bearing for damage and wear. » If the wheel bearing is damaged or worn: – Change the rear wheel bearing. – Clean and grease shaft seal rings and contact surfaces of the spacers. Long-life grease ( p.

  • Page 98: Checking The Tire Condition

    DOT number. The first two digits indicate the week of manufacture and the last two digits the year of manu- facture. KTM recommends that the tires be changed after 5 years at the latest, regardless of the actual state of H01144-01 wear.

  • Page 99: Checking Spoke Tension

    Other spokes will become looser as a result. – Check spoke tension regularly, and in particular on a new vehicle. (Your authorized KTM workshop will be glad to help.) –...

  • Page 100: 14 Electrical System

    14 ELECTRICAL SYSTEM 14.1 Removing the 12-V battery (125 XC US) Warning Risk of injury 12 V batteries contain harmful substances. – Keep 12 V batteries out of the reach of children. – Keep sparks and open flames away from 12 V batteries. –...

  • Page 101: Charging The 12-V Battery (125 Xc Us)

    ELECTRICAL SYSTEM 14 Finishing work – Mount the seat. ( p. 61) 14.3 Charging the 12-V battery (125 XC US) Warning Risk of injury 12 V batteries contain harmful substances. – Keep 12 V batteries out of the reach of children. –...

  • Page 102: Changing Main Fuse (125 Xc Us)

    It is also impossible to overcharge the 12-V battery with this battery charger. The charging time may be longer at low temperatures. This battery charger is only suitable for lithium iron phosphate batteries. Read the accompanying KTM Power Parts instruc- tions. Info Never remove cover –...
  • Page 103 ELECTRICAL SYSTEM 14 Main work – Pull starter relay from the holder. F00161-10 – Take off protection caps – Remove faulty main fuse Info A faulty fuse has a burned-out fuse wire A spare fuse is located in the starter relay. –...

  • Page 104: 15 Cooling System

    15 COOLING SYSTEM 15.1 Cooling system Water pump in the engine ensures forced circulation of the coolant. The pressure resulting from the warming of the cooling system is regulated by a valve in radiator cap . This ensures that operat- ing the vehicle at the specified coolant temperature will not result in a risk of malfunctions.

  • Page 105: Removing The Radiator Cover

    COOLING SYSTEM 15 – Position the matching radiator cover ( p. 102). The larger holding lug is located at the top left. Info Do not use both radiator covers at the same time. H01341-10 – Position radiator shield – Mount and tighten screws Guideline Remaining screws, 10 Nm (7.4 lbf ft)

  • Page 106: Checking The Coolant Level

    15 COOLING SYSTEM Warning Danger of poisoning Coolant is toxic and a health hazard. – Keep coolant out of the reach of children. – Do not allow coolant to come into contact with the skin, the eyes and clothing. – Consult a doctor immediately if coolant is swallowed. –...

  • Page 107: Draining The Coolant

    COOLING SYSTEM 15 Condition The engine is cold. – Stand the motorcycle upright on a horizontal surface. – Remove the radiator cap. – Check the coolant level in the radiator. 10 mm (0.39 in) Coolant level above the radiator fins »...

  • Page 108: Refilling With Coolant

    15 COOLING SYSTEM 15.8 Refilling with coolant Warning Danger of poisoning Coolant is toxic and a health hazard. – Keep coolant out of the reach of children. – Do not allow coolant to come into contact with the skin, the eyes and clothing. –...

  • Page 109: Changing The Coolant

    COOLING SYSTEM 15 15.9 Changing the coolant Warning Danger of scalding During motorcycle operation, the coolant gets very hot and is under pressure. – Do not open the radiator, the radiator hoses or other cooling system components if the engine or the cooling system are at operating temperature.
  • Page 110 15 COOLING SYSTEM – Mount radiator cap Danger Danger of poisoning Exhaust gases are toxic and inhal- ing them may result in unconsciousness and death. – Always make sure there is sufficient ventilation when running the engine. – Use effective exhaust extraction when starting or running the engine in an enclosed space.

  • Page 111: Tuning The Engine 16

    TUNING THE ENGINE 16 16.1 Checking throttle cable play – Check the throttle grip for smooth operation. – Move the handlebar to the straight-ahead position. Turn the throttle grip back and forth slightly and determine the play in throttle cable Throttle cable play 2 …...

  • Page 112: Carburetor Tuning

    16 TUNING THE ENGINE – Turn barrel adjuster so that there is play in the throttle cable at the throttle grip. Guideline Throttle cable play 2 … 3 mm (0.08 … 0.12 in) – Tighten nut – Slide on sleeve 400192-11 Finishing work –...
  • Page 113 TUNING THE ENGINE 16 Idling jet IJ The idling jet has the greatest influence in the low to mid throttle slide range. If the engine stutters at idle speed or when accelerating with a partially open throttle slide, a smaller idling jet must be used.

  • Page 114: Carburetor - Idle Setting

    16 TUNING THE ENGINE 402674-01 Column 2 corresponds to a needle in the standard position. Column 1 corresponds to a needle which is half a clip leaner. Column 3 corresponds to a needle which is half a clip richer. Column 4 specifies the diameter of the first cylindrical part of the needle. The smaller the diameter of the first cylindrical part of the needle, the richer the mixture preparation.

  • Page 115: Carburetor - Adjusting The Idle Speed

    TUNING THE ENGINE 16 16.5 Carburetor - adjusting the idle speed – Screw in idle air adjusting screw all the way and turn it to the specified basic setting. Info The basic adjustment is shown under the respective model. – Run the engine until warm.

  • Page 116: Plug-In Connector Of Ignition Timing Map Adjustment

    16 TUNING THE ENGINE 16.6 Plug-in connector of ignition timing map adjustment (All SX models) Plug-in connector of the ignition timing map adjustment is located on the frame under the fuel tank. K01181-10 (125 XC US) Plug-in connector of the ignition timing map adjustment is located on the frame under the fuel tank.

  • Page 117: Adjusting The Basic Position Of The Shift Lever

    TUNING THE ENGINE 16 – Sit on the vehicle in the riding position and determine distance between the upper edge of your boot and the shift lever. Distance between shift lever 10 … 20 mm (0.39 … and upper edge of boot 0.79 in) »...

  • Page 118: 17 Service Work On The Engine

    17 SERVICE WORK ON THE ENGINE 17.1 Emptying the carburetor float chamber Danger Fire hazard Fuel is highly flammable. The fuel in the fuel tank expands when warm and can escape if overfilled. – Do not fuel the vehicle in the vicinity of open flames or lit cigarettes. –...

  • Page 119: Checking The Gear Oil Level

    SERVICE WORK ON THE ENGINE 17 17.2 Checking the gear oil level Info The gear oil level must be checked when the engine is cold. Preparatory work – Stand the motorcycle upright on a horizontal surface. Main work – Remove gear oil level monitoring screw –...

  • Page 120: Adding The Gear Oil

    17 SERVICE WORK ON THE ENGINE Main work – Remove gear oil drain plug with magnet. – Remove gear oil drain plug – Let the gear oil drain fully. – Thoroughly clean the gear oil drain plug. – Clean the sealing surface on the engine. –...
  • Page 121 SERVICE WORK ON THE ENGINE 17 Main work – Remove gear oil level monitoring screw K01182-10 – Remove filler plug with the O-ring. – Add gear oil until it emerges from the drill hole of the gear oil level monitoring screw. Engine oil (15W/50) ( p.

  • Page 122: 18 Cleaning, Care

    18 CLEANING, CARE 18.1 Cleaning the motorcycle Note Material damage Components become damaged or destroyed if a pressure cleaner is used incorrectly. The high pressure forces water into the electrical components, connectors, throttle cables, and bearings, etc. Pressure which is too high causes malfunctions and destroys components. –...
  • Page 123 CLEANING, CARE 18 – After the motorcycle has cooled down, lubricate all moving parts and pivot points. – Clean the chain. ( p. 70) – Treat bare metal (except for brake discs and the exhaust sys- tem) with a corrosion inhibitor. Preserving materials for paints, metal and rubber p.

  • Page 124: 19 Storage

    96) – Store the vehicle in a dry location that is not subject to large fluctuations in temperature. Info KTM recommends jacking up the motorcycle. – Raise the motorcycle with a lift stand. ( p. 49) – Cover the vehicle with a tarp or similar cover that is permeable to air.

  • Page 125: Preparing For Use After Storage

    STORAGE 19 19.2 Preparing for use after storage – Remove the motorcycle from the lift stand. ( p. 49) – Perform checks and maintenance measures when preparing for use. ( p. 30) – Take a test ride. 401059-01...

  • Page 126: 20 Troubleshooting

    20 TROUBLESHOOTING Faults Possible cause Action – The engine cannot be cranked Operating error Carry out start procedure. ( p. 30) (starter motor) – 12-V battery discharged Charge the 12-V battery. p. 99) (125 XC US) – Check the charging voltage. –...
  • Page 127 TROUBLESHOOTING 20 Faults Possible cause Action – Engine has too little power Exhaust system leaky, Check exhaust system for damage. deformed or too little glass – Change the glass fiber yarn filling in fiber yarn filling in main the main silencer. p.

  • Page 128: 21 Technical Data

    21 TECHNICAL DATA 21.1 Engine 21.1.1 All 125 models Design 1-cylinder 2-stroke engine, water-cooled, with reed intake and exhaust control Displacement 124.8 cm³ (7.616 cu in) Stroke 54.5 mm (2.146 in) Bore 54 mm (2.13 in) Crankshaft bearing 1 grooved ball bearing/1 roller bearing Conrod bearing Needle bearing Piston pin bearing...

  • Page 129: Engine Tightening Torques

    TECHNICAL DATA 21 Clutch Multidisc clutch in oil bath/hydraulically activated Gearbox 6-gear transmission, claw shifted Transmission ratio first-gear 14:32 second-gear 15:30 third-gear 17:28 fourth-gear 19:27 fifth-gear 19:23 sixth-gear 22:24 Ignition Contactless controlled fully electronic ignition with digital ignition adjustment Spark plug NGK BR9 ECMVX Spark plug electrode gap 0.60 mm (0.0236 in)
  • Page 130 21 TECHNICAL DATA Screw, intake flange/reed valve 6 Nm (4.4 lbf ft) housing Screw, intermediate clutch cover M6x20 10 Nm (7.4 lbf ft) Screw, intermediate clutch cover M6x25 10 Nm (7.4 lbf ft) Screw, intermediate clutch cover M6x30 10 Nm (7.4 lbf ft) Screw, kick starter stop plate 10 Nm (7.4 lbf ft) Loctite...

  • Page 131: Carburetor

    TECHNICAL DATA 21 21.3 Carburetor 21.3.1 125 SX Carburetor type MIKUNI TMX 38 Carburetor identification number TMX 38 87 Needle position 2nd position from top Jet needle 6BFY43‑71 (6BFY42‑71) Main jet 500 (480, 490, 520, 540, 560) Idling jet 35 (30 / 32.5 / 37.5 / 40) Choke nozzle Needle jet S‑7...

  • Page 132: Carburetor - Basic Setting For Sandy Surfaces (All 125 Models)

    21 TECHNICAL DATA Needle position from top Main jet Info Do not use on sandy terrain. 21.3.3 Carburetor - basic setting for sandy surfaces (All 125 models) Idle air adjusting screw Open 2 turns Idling jet 37.5 Jet needle 6BFY42‑71 Needle position 3rd position from top Main jet...

  • Page 133: Carburetor Tuning (150 Sx)

    TECHNICAL DATA 21 21.3.4 150 SX Carburetor type MIKUNI TMX 38 Carburetor identification number TMX 38 88 Needle position 3rd position from top Jet needle 6BFY42‑71 (6BFY43‑71) Main jet 470 (460, 480, 490, 500, 520) Idling jet 30 (25 / 27.5 / 32.5 / 35) Choke nozzle Needle jet S‑4...

  • Page 134: Basic Carburetor Setting For Sandy Surfaces (150 Sx)

    21 TECHNICAL DATA Info Do not use on sandy terrain. 21.3.6 Basic carburetor setting for sandy surfaces (150 SX) Idle air adjusting screw Open 2 turns Idling jet 37.5 Jet needle 6BFY42‑71 Needle position 3rd position from top Main jet Info If the engine is not running smoothly, use a smaller main jet.

  • Page 135: 125 Xc Us

    TECHNICAL DATA 21 21.3.7 125 XC US Carburetor type MIKUNI TMX 38 Carburetor identification number TMX 38 77 Needle position 2nd position from top Jet needle 6BFY43‑75 (6BFY42‑71 / 6BFY43‑71) Main jet 470 (480, 490, 500, 520, 540) Idling jet 32.5 (30 / 35 / 37.5 / 40) Choke nozzle Needle jet...

  • Page 136: Carburetor - Basic Setting For Sandy Surfaces (All 125 Models)

    21 TECHNICAL DATA Main jet Info Do not use on sandy terrain. For fast circuits with a large portion of high-load riding MIKUNI TMX 38 −6 … 5 °C 6 … 15 °C 16 … 24 °C 25 … 36 °C 37 …...

  • Page 137: Capacities

    TECHNICAL DATA 21 Idling jet 37.5 Jet needle 6BFY42‑71 Needle position 3rd position from top Main jet Info If the engine is not running smoothly, use a smaller main jet. 21.4 Capacities 21.4.1 Gear oil Gear oil 0.80 l (0.85 qt.) Engine oil (15W/50) ( p.

  • Page 138: Electrical System

    110/100 - 18 64M TT Dunlop GEOMAX AT 81 F Dunlop GEOMAX AT 81 The tires specified represent one of the possible series production tires. Additional information is available in the Service section under: http://www.ktm.com 21.8 Fork 21.8.1 All SX models Fork article number 34.18.8U.01...

  • Page 139: Xc Us

    TECHNICAL DATA 21 Oil capacity external mechanism ml (7.78 fl. oz.) Fork oil (SAE 4) (48601166S1) + 10 + 0.34 − 50 − 1.69 right p. 142) Grease capacity, left cartridge 5 g (0.18 oz) Special grease (00062010053) p. 144) Oil capacity, right cartridge 380 ml (12.85 fl.

  • Page 140: Xc Us

    21 TECHNICAL DATA Spring preload 7 mm (0.28 in) Spring rate Weight of rider: 65 … 75 kg (143 … 165 lb.) 36 N/mm (206 lb/in) Weight of rider: 75 … 85 kg (165 … 187 lb.) 39 N/mm (223 lb/in) Weight of rider: 85 …...

  • Page 141: Chassis Tightening Torques

    TECHNICAL DATA 21 21.10 Chassis tightening torques Screw, switch-off button 0.4 Nm (0.3 lbf ft) Screw, fixed grip 5 Nm (3.7 lbf ft) Loctite ® 243™ Screw, service hour counter 0.8 Nm (0.59 lbf ft) Spoke nipple, front wheel M4.5 6 Nm (4.4 lbf ft) Spoke nipple, rear wheel M4.5...
  • Page 142 21 TECHNICAL DATA Screw, top steering stem 20 Nm (14.8 lbf ft) Loctite ® 243™ Screw, top triple clamp 17 Nm (12.5 lbf ft) Engine bracket screw 60 Nm (44.3 lbf ft) Remaining nuts, chassis 45 Nm (33.2 lbf ft) Remaining screws, chassis 45 Nm (33.2 lbf ft) Screw, bottom shock absorber...

  • Page 143: Substances 22

    SUBSTANCES 22 Brake fluid DOT 4 / DOT 5.1 Standard/classification – Guideline – Use only brake fluid that complies with the specified standard (see specifications on the container) and that exhibits the corresponding properties. Recommended supplier Castrol – REACT PERFORMANCE DOT 4 MOTOREX ®...
  • Page 144 22 SUBSTANCES Recommended supplier MOTOREX ® – Cross Power 2T Fork oil (SAE 4) (48601166S1) Standard/classification – SAE ( p. 145) (SAE 4) Guideline – Use only oils that comply with the specified standards (see specifications on the container) and that exhibit the corresponding properties.

  • Page 145: Auxiliary Substances 23

    AUXILIARY SUBSTANCES 23 Air filter cleaner Recommended supplier MOTOREX ® – Racing Bio Dirt Remover Chain cleaner Recommended supplier MOTOREX ® – Chain Clean Fuel additive Recommended supplier MOTOREX ® – Fuel Stabilizer High viscosity grease Recommended supplier ® – LGHB 2 Long-life grease Recommended supplier...
  • Page 146 23 AUXILIARY SUBSTANCES Special cleaner for glossy and matte paint finishes, metal and plastic surfaces Recommended supplier MOTOREX ® – Quick Cleaner Special grease (00062010053) Recommended supplier Klüber Lubrication ® – KLÜBERFOOD NH1 34‑401 Universal oil spray Recommended supplier MOTOREX ®...

  • Page 147: Standards 24

    STANDARDS 24 JASO T903 MA2 Different technical development directions required a separate specification for motorcycles – the JASO T903 MA2 standard. Earlier, engine oils from the automobile industry were used for motorcycles because there was no separate motor- cycle specification. Whereas long service intervals are demanded for automobile engines, the focus for motorcycle engines is on high performance at high engine speeds.

  • Page 148: 25 List Of Abbreviations

    25 LIST OF ABBREVIATIONS Art. no. Article number circa compare e.g. for example etc. et cetera i.a. inter alia number poss. possibly...

  • Page 149: Index

    INDEX Carburetor tuning ..... . 110 INDEX Chain 12 V battery checking ......72 installing .
  • Page 150 INDEX Foot brake lever ......20 basic position, adjusting ....86 Ignition timing map free travel, checking .
  • Page 151 INDEX removing ......93 chassis tightening torques ... . . 139 electrical system .
  • Page 152 *3214209en* 3214209en 06/2020 KTM Sportmotorcycle GmbH 5230 Mattighofen/Austria Photo: Mitterbauer/KISKA/KTM http://www.ktm.com...

This manual is also suitable for:

150 sx 2021125 xc 2021F6101u0F6101u1F6175u3

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