![background image](http://html.mh-extra.com/html/stihl/fs-25-4/fs-25-4_user-manual_1379255008.webp)
2.
Erratic running behavior at low rpm
Inspect air filter element.
Not dirty
Remove spark plug and
check electrodes for coking,
check electrode gap.
Normal
Check to see if fuel line is kin-
ked, pinched or cracked. Check
carburetor for looseness or air
entering through spacer flange.
Normal
Check fuel filter.
Not dirty
Check correct function of
carburetor.
Normal
Check compression.
Normal
Start engine according to
instructions.
Dirty
Abnormal
Abnormal
Dirty
Abnormal
Abnormal
Clean, replace air filter
element.
– Clean spark plug and
adjust electrode gap.
– Replace spark plug.
– If fuel line is kinked
or pinched, fit a
new one.
– Tighten loose carburetor
nuts. Examine spacer
flange for damage and
install properly.
Clean, replace filter.
Replace carburetor.
– Check, adjust valve
clearance.
– Check combustion chamber
for excessive build-up of
combustion deposits.
– Check valves for faults.
– Check piston, rings and
cylinder for wear.
8
FS 25-4, 65-4