KTM 450 SX 2009 Owner's Manual page 158

MAINTENANCE ON CHASSIS AND ENGINE
–
Adjust the idle speed with adjusting screw
Guideline
Choke function deactivated – The choke lever is pushed in to the stop. (
Idle speed
Info
If the idle speed is set significantly higher, the engine does not start. When the
electric starter button is activated, the electric starter turns over the engine, but
the engine does not start because there is no ignition spark.
–
Turn idle adjusting screw
–
Note the position and turn the idle adjusting screw slowly counterclockwise until the
idle speed falls.
–
Adjust to the point between these two positions with the highest idle speed.
Info
If there is a big engine speed rise, reduce the idle speed to a normal level and
repeat the above steps.
The extremely sporty rider will set the mixture about 1/4 of a turn back from this
ideal value (leaner, in a clockwise direction) since the engine becomes hotter in
sporting use.
If the procedure described here does not lead to satisfactory results, the cause
may be a wrongly dimensioned idling jet.
If you can turn the idle adjusting screw to the end without any change of engine
speed, you have to fit a smaller idling jet.
The idle adjusting screw must not be opened more than two turns. If more than
two turns are necessary (rich mixture), use a larger idling jet.
After changing the idling jet, start from the beginning with the adjusting steps.
.

1,500... 1,600 rpm
slowly until the idle speed begins to fall.

156
p. 38)