Stihl MS 231 Manual page 18

Condition
Engine speed drops quickly under
load – low power
Engine running extremely rich, has
no power and a very low maximum
speed
MS 231, MS 231 C, MS 251, MS 251 C
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Cause
Air filter dirty
Throttle shutter not opened fully
Tank vent faulty
Fuel pickup body dirty
Fuel strainer dirty
Leak on fuel hose from tank to
carburetor
Setting of high speed screw H too
rich
Main jet bores or ports blocked
Pump diaphragm damaged or
fatigued
Ignition timing wrong, flywheel out
of adjustment
– key in flywheel has sheared off
Choke shutter does not open
Remedy
Clean air filter or replace if
necessary
Check throttle rod
Replace tank vent
Install new pickup body
Clean fuel strainer in carburetor,
replace if necessary
Seal connections or install new fuel
hose
Check basic carburetor setting,
correct if necessary
Clean the carburetor
Fit new pump diaphragm
Install new flywheel
Check carburetor and choke shaft,
service or replace if necessary
17