Stihl MS 390 - STIHL MS 290, 310, 390 Carburetor Troubleshooting

11MS 290, MS 310, MS 390
4.5 Carburetor
Condition Cause Remedy
Carburetor floods;
engine stalls
Inlet needle not sealing. Foreign
matter in valve seat or cone
damaged
Remove and clean or replace the
inlet needle, clean the fuel tank,
pickup body and fuel line if
necessary
Inlet control lever sticking on
spindle
Free off inlet control lever
Helical spring not located on nipple
of inlet control lever
Remove the inlet control lever and
refit it correctly
Perforated disc on diaphragm is
deformed and presses constantly
against the inlet control lever
Fit a new metering diaphragm
Inlet control lever too high
(relative to correct installed
position)
Set inlet control lever flush with top
edge of housing
Poor acceleration Idle jet too lean Rotate low speed screw (L)
counterclockwise (richer), no
further than stop
Main jet too lean Rotate high speed screw (H)
counterclockwise (richer), no
further than stop
Inlet control lever too low
(relative to correct installed
position)
Set inlet control lever flush with top
edge of housing
Inlet needle sticking to valve seat Remove inlet needle, clean and
refit
Diaphragm gasket leaking Fit new diaphragm gasket
Metering diaphragm damaged or
shrunk
Fit new metering diaphragm
Impulse hose damaged or kinked Fit new impulse hose