15MS 171, MS 181, MS 211
Condition Cause Remedy
Engine will not idle,
idle speed too high
Throttle shutter opened too wide by
idle speed screw (LA)
Reset idle speed screw (LA)
correctly
Oil seals/engine leaking Seal or replace oil seals/
engine
Air valve contaminated
– does not close
Clean air valve, replace if
necessary
Air valve stiff Check air valve, replace if
necessary
Throttle rod stiff
– throttle shutter does not close
Replace throttle rod and lever
Engine stalls at idle speed Idle jet bores or ports blocked Clean the carburetor
Idle jet too rich or too lean Set low speed screw (L)
correctly
Setting of idle speed (LA)
incorrect – throttle shutter
completely closed
Set idle speed screw (LA)
correctly