Stihl FS 94 Instruction Manual page 13

Condition
Engine loses power during
acceleration
Engine will not idle, idle speed too
high
Engine stops while idling
12
Cause
Jet on the
low speed screw L dirty –
insufficient volume of fuel, engine
running too lean
Fuel strainer dirty
Control valve opened too wide by
idle speed screw (LA)
Oil seals / crankcase leaking
Cylinder gasket leaking
Gaskets on spacer flange and
carburetor leaking, or crack in
spacer flange
Spring in control valve broken or
fatigued – throttle lever is not
returned to original position
Setting of low speed screw (L) too
rich or too lean
Setting of idle speed screw LA
incorrect – control valve completely
closed
Control valve lever does not locate
against
idle speed screw LA
– control valve completely closed
Tank vent faulty
Leak in fuel hose from tank to
carburetor
Remedy
Clean the carburetor
Clean fuel strainer and carburetor
Reset idle speed screw (LA)
correctly
Seal oil seals / crankcase, replace if
necessary
Perform leakage test, inspect
sealing faces and replace cylinder
gasket if necessary
Perform leakage test, replace
gaskets and spacer flange if
necessary
Install new control valve, check and
replace carburetor if necessary
Reset low speed screw (L)
correctly
Reset idle speed screw (LA)
correctly
Open the throttle wide, the control
valve lever returns to its original
position and locates against the idle
speed screw (LA), replace control
valve if necessary
Fit new tank vent
Install a new fuel suction hose.
Series 4149 Powerhead