Engine - Stihl MS 650 Manual

4.6

Engine

Always check and, if necessary,
repair the following parts before
looking for faults on the engine:
– Air filter
– Fuel system
– Carburetor
– Ignition system
Condition
Engine does not start easily, stalls
at idle speed, but operates normally
at full throttle
Engine does not deliver full power
or runs erratically
Engine overheating
MS 650, MS 660
Cause
Oil seals in crankcase damaged
Crankcase leaking or damaged
(cracks)
Piston rings worn or broken
Muffler / spark arresting screen
carbonized
Air filter element dirty
Fuel / impulse hose severely kinked
or damaged
Decompression valve sticking
Insufficient cylinder cooling. Air
inlets in fan housing blocked or
cooling fins on cylinder very dirty
Remedy
Replace the oil seals
Seal or replace the crankcase
Fit new piston rings
Clean the muffler (inlet and
exhaust), replace spark arresting
screen, replace muffler if
necessary
Replace air filter element
Fit new hoses or position them free
from kinks
Replace the decompression valve
Thoroughly clean all cooling air
openings and the cylinder fins
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