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KTM 125 SX - User Manual

KTM 125 SX
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OWNER'S MANUAL 2016
125 SX
150 SX
250 SX
250 XC
300 XC
Art. no. 3213330en

Table of Contents

Other manuals for KTM 125 SX

Questions and Answers

  • K
    Kimberly EllisonAug 14, 2025
    What to do if my KTM 125 SX engine turns but does not start?
    • S
      Steven BakerAug 14, 2025
      If your KTM Motorcycle engine turns over but fails to start, several factors could be at play. It could be an operating error, so ensure you're following the correct starting procedure. If the motorcycle has been stored for a while, old fuel in the float chamber might be the culprit; in this case, empty the carburetor float chamber. Also, inspect the spark plug; if it's oily or wet, clean and dry it, or replace it if necessary. Check the spark plug electrode gap and adjust to 0.60 mm (0.0236 in). Inspect the socket connector or ignition coil and clean the plug-in connector and treat it with contact spray. Finally, water in the carburetor or blocked jets can prevent starting, so check/set the carburetor components.
  • J
    James McguireAug 17, 2025
    How to fix KTM 125 SX engine that does not speed up?
    • J
      Julia FernandezAug 17, 2025
      If your KTM Motorcycle engine isn't speeding up, the carburetor might be running over due to a dirty or worn float needle, so check/set the carburetor components. Loose carburetor jets can also cause this issue; check/set the carburetor components. A fuel feed interruption could be the problem; check the fuel tank breather, clean the fuel tap, and check/set the carburetor components. A very dirty air filter can restrict airflow, so clean the air filter and air filter box. Lastly, a leaky or deformed exhaust system, or one with insufficient glass fiber yarn filling in the main silencer, can cause this; check the exhaust system for damage and change the glass fiber yarn filling of the main silencer.
  • B
    Brett BlairAug 21, 2025
    What to do if KTM 125 SX Motorcycle engine cannot be cranked?
    • T
      Troy WilliamsAug 21, 2025
      If your KTM Motorcycle engine fails to crank, there are several potential causes. You may be experiencing an operating error, so go through the steps of starting the engine. The battery could be discharged, so recharge the battery. The main fuse might be blown; remove and install the main fuse. A faulty starter relay or starter motor could also be the issue, so check the starter relay and starter motor.
  • K
    Keith AdamsAug 25, 2025
    Why does my KTM 125 SX engine overheat?
    • M
      Michael ElliottAug 25, 2025
      Several issues can cause your KTM Motorcycle engine to overheat. The cooling system may have too little coolant due to leakage, so check the system and coolant level. Foam formation in the cooling system can also lead to overheating; drain and refill the coolant. Inspect the radiator hose for bends and replace if necessary. Finally, an incorrect ignition point due to a loose stator can cause overheating, so adjust the ignition.
  • K
    Krista DavisAug 27, 2025
    Why KTM 125 SX Motorcycle engine has no idle?
    • J
      Jose MunozAug 28, 2025
      A KTM Motorcycle engine with no idle could be due to several reasons. The idling jet might be blocked, so check/set the carburetor components. Adjusting screws on the carburetor could be distorted, so adjust the idle speed. The spark plug could also be defective, so change the spark plug.
  • G
    gvalenzuelaAug 31, 2025
    What causes KTM 125 SX engine to stall or pop into the carburetor?
    • R
      Rebecca JohnstonAug 31, 2025
      If your KTM Motorcycle engine stalls or pops into the carburetor, it's likely due to a lack of fuel. For all SX and XC models, ensure the fuel tap is in the ON position and refuel if necessary.
  • M
    Mary FieldsSep 3, 2025
    What does it mean if there is white smoke emission in KTM 125 SX Motorcycle?
    • J
      joshuavelasquezSep 3, 2025
      White smoke emission, or steam, in the exhaust gas of your KTM Motorcycle indicates a damaged cylinder head or cylinder head gasket. You should check the cylinder head or cylinder head gasket.
  • M
    Michael StevensSep 6, 2025
    Why gear oil exits at the vent hose of KTM 125 SX?
    • M
      Meghan HallSep 6, 2025
      Gear oil exiting at the vent hose of your KTM Motorcycle typically means too much gear oil was added. Check the gear oil level.
  • A
    Allison FieldsSep 10, 2025
    How to fix water in the gear oil of KTM 125 SX?
    • B
      Brian HubbardSep 10, 2025
      Water in the gear oil of your KTM Motorcycle suggests a damaged shaft seal ring or water pump. Check the shaft seal ring and water pump.

Summary

2 Safety Advice

2.1 Use Definition - Intended Use

Defines intended use for SX and XC models, differentiating usage environments.

2.2 Safety Advice

General safety instructions and importance of warning labels on the vehicle.

2.3 Degrees of Risk and Symbols

Defines danger levels (Danger, Warning, Caution, Note) and associated symbols.

2.5 Safe Operation

Covers general safe operating practices, including impairment, poisoning, and burns.

2.6 Protective Clothing

Emphasizes the importance of wearing appropriate protective clothing for safety.

6 Controls

6.4 Kill Switch

Explains the kill switch function and its possible states for engine operation.

7 Preparing for Use

7.1 Advice on First Use

Provides critical safety advice and pre-ride checks for new users.

7.2 Running in the Engine

Guides on engine break-in procedures to ensure optimal performance and longevity.

8 Riding Instructions

8.1 Checks and Maintenance Work When Preparing for Use

Lists essential checks and maintenance before riding for operating safety.

8.2 Starting

Details the procedure for starting the engine, including safety warnings and cold engine considerations.

8.3 Starting Off

Explains the steps for moving off from a standstill, including clutch and throttle control.

8.4 Shifting, Riding

Covers gear shifting techniques, riding advice, and handling unusual noises.

8.5 Braking

Provides instructions and warnings related to braking, including adapting to conditions.

8.6 Stopping, Parking

Details procedures for safely stopping and parking the motorcycle, including warnings.

8.8 Refueling

Covers safe refueling practices, fuel types, and tank capacity information.

9 Service Schedule

9.1 All SX Models Service Schedule

Outlines periodic maintenance tasks for SX models based on operating hours/races.

9.2 All XC Models Service Schedule

Details periodic maintenance tasks for XC models based on operating hours/races.

10 Tuning the Chassis

10.1 Checking the Basic Chassis Setting with the Riders Weight

Explains how to adjust chassis settings based on rider weight for optimal performance.

10.4 Adjusting the Low-Speed Compression Damping of the Shock Absorber

Details how to adjust the low-speed compression damping of the shock absorber.

10.5 Adjusting the High-Speed Compression Damping of the Shock Absorber

Provides instructions for adjusting the high-speed compression damping of the shock absorber.

10.6 Adjusting the Rebound Damping of the Shock Absorber

Explains the procedure for adjusting the rebound damping of the shock absorber.

10.9 Checking the Riding Sag of the Shock Absorber

Explains the process for checking the riding sag with the rider's weight.

10.10 Adjusting the Spring Preload of the Shock Absorber

Provides instructions for adjusting the spring preload on the rear shock absorber.

10.11 Adjusting the Riding Sag

Guides on how to adjust the riding sag of the shock absorber.

10.13 Adjusting the Fork Air Pressure (125;150 SX EU)

Details how to adjust the air pressure in the front fork for the 125/150 SX EU models.

10.14 Adjusting the Compression Damping of the Fork

Explains how to adjust the compression damping on the front fork for various models.

10.15 Adjusting the Rebound Damping of the Fork

Details how to adjust the rebound damping on the front fork for various models.

11 Service Work on the Chassis

11.12 Adjusting the Steering Head Bearing Play

Details the procedure for adjusting the steering head bearing play.

11.36 Checking the Chain Tension

Guides on how to check and adjust the drive chain tension, with safety warnings.

11.37 Adjusting the Chain Tension

Provides instructions for adjusting the drive chain tension.

12 Brake System

12.1 Checking the Free Travel of the Hand Brake Lever

Explains how to check the free travel of the front brake lever.

12.4 Checking the Front Brake Fluid Level

Explains how to check the front brake fluid level and warnings.

12.5 Adding Front Brake Fluid

Provides instructions for adding front brake fluid, including safety precautions.

12.6 Checking the Front Brake Linings

Guides on checking the front brake linings for wear and damage.

12.7 Changing the Front Brake Linings

Details the procedure for changing the front brake linings.

12.8 Checking the Free Travel of Foot Brake Lever

Explains how to check the free travel of the rear brake lever.

12.10 Checking the Rear Brake Fluid Level

Explains how to check the rear brake fluid level and warnings.

12.11 Adding Rear Brake Fluid

Provides instructions for adding rear brake fluid, including safety precautions.

12.12 Checking the Rear Brake Linings

Guides on checking the rear brake linings for wear and damage.

12.13 Changing the Rear Brake Linings

Details the procedure for changing the rear brake linings.

13 Wheels, Tires

13.6 Checking the Tire Air Pressure

Guides on checking and setting correct tire air pressure for optimal performance.

14 Electrical System

14.4 Change the Main Fuse (All XC Models)

Explains how to locate and change the main fuse, including safety precautions.

15 Cooling System

15.5 Checking the Antifreeze and Coolant Level

Guides on checking coolant level and antifreeze protection, with safety warnings.

15.6 Checking the Coolant Level

Explains how to check the coolant level in the radiator, with safety warnings.

16 Tuning the Engine

16.2 Adjusting the Play in the Throttle Cable

Provides instructions for adjusting throttle cable play for optimal performance.

16.3 Carburetor - Idle

Explains the influence of idle settings on engine behavior and lists factory settings.

16.4 Carburetor - Adjusting the Idle Speed

Details how to adjust the engine idle speed using specific screws.

16.6 Changing the Ignition Timing Map

Explains how to switch between 'Soft' and 'Performance' ignition timing maps.

17 Service Work on the Engine

17.2 Checking the Gear Oil Level

Explains how to check the engine gear oil level when the engine is cold.

17.5 Refilling with Gear Oil

Guides on refilling the engine with the correct gear oil, including capacity.

19 Storage

20 Troubleshooting

Engine Cannot Be Cranked

Lists possible causes and actions for when the engine won't crank.

Engine Turns But Does Not Start

Addresses issues when the engine cranks but fails to start.

Engine Has No Idle

Outlines causes and solutions for lack of proper engine idling.

Engine Does Not Speed Up

Provides troubleshooting steps for acceleration issues.

Engine Has Too Little Power

Identifies causes and fixes for reduced engine power.

Engine Stalls or Pops Into Carburetor

Addresses issues related to engine stalling or backfiring.

Engine Overheats

Lists causes and solutions for engine overheating problems.

21 Technical Data

Engine Tightening Torques

Lists critical torque values for engine components to ensure proper assembly.

Carburetor Specifications and Tuning

Details carburetor settings and tuning charts for various conditions and models.

Fork Specifications

Provides detailed specifications for the front fork, including damping and air pressure.

Shock Absorber Specifications

Lists detailed specifications for the rear shock absorber, including damping and sag.

Chassis Tightening Torques

Lists critical torque values for chassis components to ensure proper assembly.

22 Substances

KTM 125 SX Specifications

General IconGeneral
Engine Type1-cylinder, 2-stroke engine
Displacement124.8 cm³
Bore/Stroke54 mm / 54.5 mm
StarterKickstarter
Transmission6-speed
Rear SuspensionWP XACT shock absorber with linkage
Front BrakeDisc brake
Rear BrakeDisc brake
Ground Clearance375 mm
Seat Height950 mm
CoolingLiquid cooled
Front SuspensionWP XACT USD, Ø 48 mm
Fuel SystemCarburetor
ClutchWet multi-disc clutch
FrameCentral double-cradle type in chrome-molybdenum steel

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