Stihl FS 240 Service Manual page 17

Problem
Cutting attachment stops when
idling, versions without M-Tronic
... All versions
... Versions with M-Tronic
Engine speed drops quickly under
load – low power,
all versions
... Versions without M-Tronic
16
Cause
Idle speed too high
Clutch springs stretched or fatigued Replace tension springs, replace
Clutch spring hooks broken
Parts in carburetor or M-Tronic
wiring harness defective
Air filter dirty
Throttle shutter not opened fully
Tank vent faulty
Fuel pick-up body dirty
Fuel strainer dirty
Leak in fuel line between tank and
carburetor
Main jet bores or ports blocked
Pump diaphragm damaged or
fatigued
Incorrect ignition timing, flywheel
out of adjustment
– Key in flywheel has sheared off
High speed screw H "too rich"
FS 240 C, FS 260 C, FS 360 C, FS 410 C, FS 460 C-M
Remedy
Readjust with idle speed screw
LA (counterclockwise)
clutch if necessary
Replace tension springs
Carry out M-Tronic diagnosis, if
necessary, replace carburetor or
M-Tronic wiring harness
Clean air filter, replace if necessary
Check throttle cable and rod
Replace tank vent
Replace pickup body
Clean fuel strainer in carburetor,
replace if necessary
Seal connections or replace line
Clean the carburetor
Replace pump diaphragm
Install new flywheel
Check basic carburetor setting,
correct if necessary