Stihl MS 661 Manual page 15

Condition
Engine stops while idling
Engine will not idle, idle speed too
high
14
Cause
Idle jet bores
or ports blocked
Setting of low speed screw ( L) too
rich or too lean
Setting of idle speed screw LA
incorrect – throttle shutter
completely closed
Models with M-Tronic, carburetor
setting too rich or too lean
Tank vent faulty
Leak in fuel hose between pickup
body and carburetor
Setting of idle speed screw LA
incorrect – throttle shutter opened
too wide
Models with M-Tronic, idle speed
too high
Oil seals / crankcase leaking
Throttle shutter does not close
Remedy
Clean the carburetor
Reset low speed screw (L)
correctly
Readjust idle speed screw
LA (clockwise)
Check M-Tronic with STIHL MDG 1
and troubleshooting chart, b 8.7,
adjust or calibrate control unit,
b 8.1
(setting of idle speed screw must
not be changed)
Fit new tank vent
Seal connections or install new fuel
hose
Readjust idle speed screw
LA (counterclockwise)
Check M-Tronic with STIHL MDG 1
and troubleshooting chart, b 8.7,
adjust or calibrate control unit,
b 8.1
(setting of idle speed screw must
not be changed)
Seal oil seals / crankcase, replace if
necessary
Install new carburetor
MS 661, MS 661 C-M