Adjusting The Carburetor - Stihl MS 381 Instruction Manual

Adjusting the Carburetor

General Information
The carburetor comes from the factory
with a standard setting.
This setting provides an optimum fuel-air
mixture under most operating
conditions.
Retuning may be necessary if there is a
change in barometric pressure
(weather, altitude), temperature or
humidity.
Changing the setting of the high speed
screw alters the engine's power output
and the maximum off-load engine
speed.
Standard Setting (without tachometer)
Shut off the engine.
N
Check the air filter and clean or
N
replace if necessary.
Check the spark arresting screen
N
(not in all models, country-specific)
in the muffler and clean or replace if
necessary.
Check chain tension
N
MS 381
H L
Carefully screw both adjusting
N
screws down onto their seats
(clockwise).
Turn the high speed screw (H) one
N
full turn counterclockwise.
Turn the low speed screw (L) one
N
full turn counterclockwise.
NOTICE
If you do not have a tachometer, do not
set the high speed screw any leaner by
turning it beyond the standard setting.
Fine Tuning (with tachometer)
Carry out the standard setting.
N
Start and warm up the engine.
N
Adjust idle speed correctly – the
N
chain must not rotate.
Use the high speed screw (H) to
N
adjust the maximum engine speed
to 12,500 rpm with bar and correctly
tensioned chain – use a tachometer.
Adjusting idle speed
Engine stops while idling
L
Open the low speed screw (L) one
N
full turn.
Turn the idle speed screw (LA)
N
clockwise until the chain begins to
run – then back it off 1/4 turn.
Saw chain runs while engine is idling
Open the low speed screw (L) one
N
full turn.
Turn the idle speed screw (LA)
N
counterclockwise until the chain
stops moving – then turn it another
1/4 turn in the same direction.
WARNING
If the chain continues moving when the
engine is idling, have your saw checked
and repaired by your servicing dealer.
Erratic idling behavior, poor acceleration
(even though low speed screw is open
one turn)
Idle setting is too lean
Turn the low speed screw (L)
N
counterclockwise, no further than
stop, until the engine runs and
accelerates smoothly.
English
85