KTM 125 SX User Manual (English)

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.
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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.

KTM 125 SX Specifications

General

Engine Type	1-cylinder, 2-stroke engine
Displacement	124.8 cm³
Bore/Stroke	54 mm / 54.5 mm
Starter	Kickstarter
Transmission	6-speed
Rear Suspension	WP XACT shock absorber with linkage
Front Brake	Disc brake
Rear Brake	Disc brake
Ground Clearance	375 mm
Seat Height	950 mm
Cooling	Liquid cooled
Front Suspension	WP XACT USD, Ø 48 mm
Fuel System	Carburetor
Clutch	Wet multi-disc clutch
Frame	Central double-cradle type in chrome-molybdenum steel