KTM 125 SX - Engine Stalls or Pops Into Carburetor; Engine Overheats; White Smoke Emission (Steam in Exhaust Gas)

20 TROUBLESHOOTING 110
Faults Possible cause Action
Engine stalls or is popping into the
carburetor
Lack of fuel
(All 125/150 models)
–
Turn handle

of the fuel tap to the ON
position. (Figure M01127-10 p. 14)
(250 SX)
–
Turn handle

of the fuel tap to the ON
position. (Figure B02072-10 p. 14)
(All XC models)
–
Turn handle

of the fuel tap to the ON
position. (Figure L00904-10 p. 14)
(All XC models)
–
Turn handle

of the fuel tap to the RES
position. (Figure L00904-10 p. 14)
– Refuel. ( p. 26)
Engine takes in bad air – Check the intake flange and carburetor for
tightness.
The connector or ignition coil is loose
or oxidized
– Clean the connector and treat it with contact
spray.
Engine overheats Too little coolant in cooling system – Check the cooling system for leakage.
– Check the coolant level. ( p. 94)
Too little air stream – Switch off engine when stationary.
Radiator fins very dirty – Clean the radiator fins.
Foam formation in cooling system – Drain the coolant. ( p. 94)
– Refill with coolant. ( p. 95)
Damaged cylinder head or cylinder
head gasket
– Check the cylinder head and cylinder head gas-
ket.
Bent radiator hose – Change the radiator hose.
Incorrect ignition point due to loose
stator
– Adjust the ignition.
White smoke emission (steam in
exhaust gas)
Damaged cylinder head or cylinder
head gasket
– Check the cylinder head and cylinder head gas-
ket.
Gear oil exits at the vent hose Too much gear oil added – Check the gear oil level. ( p. 103)
Water in the gear oil Damaged shaft seal ring or water
pump
– Check the shaft seal ring and water pump.