Carburetor - Stihl 4180 Series Service Manual

3.4

Carburetor

Condition
Carburetor floods, engine stalls
Poor acceleration
Engine will not idle, idle speed too
high
Engine stops while idling
Engine speed drops quickly under
load – low power
6
Cause
Inlet needle not sealing. Foreign matter in
valve seat or cone damaged
Inlet control lever sticking on spindle
Helical spring not located on nipple of inlet
control lever
Inlet control lever too high (relative to cor-
rect installed position)
Idling or full load setting too lean
Inlet control lever too low (relative to cor-
rect installed position)
Inlet needle sticking to valve seat
Diaphragm gasket damaged
Metering diaphragm damaged / shrunk /
hardened
Throttle shutter opened too wide by idle
speed screw (LA)
Throttle shutter is not closed properly even
when idle speed screw (LA) is backed off
all the way
Engine leaking
Idle jet bores or ports blocked
Setting of low speed screw (L) too rich or
too lean
Setting of idle speed screw (LA) incorrect –
throttle shutter completely closed
Air filter dirty
Exhaust port / muffler carbonized
Throttle shutter is not opened fully
Tank vent faulty
Fuel pickup body dirty
Leak in a fuel hose
Fuel strainer in carburetor dirty
Setting of high speed screw (H) too rich
Pump diaphragm damaged / shrunk /
hardened
Remedy
Remove and clean the inlet needle, clean
the carburetor
Free off inlet control lever
Remove the inlet control lever and refit it
correctly
Fit new inlet control lever
Readjust the carburetor
Fit new inlet control lever
Remove inlet needle and clean valve seat
Fit new diaphragm gasket
Fit new metering diaphragm
Reset idle speed screw (LA) correctly
Check throttle cable
Test engine for leaks
Clean the carburetor
Reset low speed screw (L) correctly
Reset idle speed screw (LA) correctly
Clean or replace air filter
Clean exhaust port / muffler, fit new muffler
if necessary
Check throttle cable
Test the tank vent, replace if necessary
Clean the pickup body, replace if
necessary
Check fuel hoses and replace if necessary
Clean fuel strainer in carburetor, replace if
necessary
Readjust the carburetor
Fit new pump diaphragm
Series 4180 Powerhead