Stihl MS 291 Product Instruction Manual - Page 43

Adjusting the Carburetor

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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. With this carburetor it is only possible to correct the adjusting screws within fine limits. If the setting is too lean there is a risk of engine damage due to insufficient lubrication and overheating. Standard Setting HL LA N Stopping the engine N Check the air filter and clean or replace if necessary. N Check the spark arresting screen (country-specific) in the muffler and clean or replace if necessary. 5902BA012 KN N Turn the high speed screw (H) counterclockwise as far as stop (no more than 3/4 turn). N Turn the low speed screw (L) carefully clockwise as far as stop, then turn it back 1 full turn. Readjust idle Engine stops while idling N Open the low speed screw (L) one full turn. N Turn the idle speed screw (LA) clockwise until the chain begins to run - then back it off 1 full turn. Chain runs when engine is idling N Open the low speed screw (L) one full turn. N Turn the idle speed screw (LA) counterclockwise until the chain begins to run - then turn it another 1 turn in the same direction. 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) N Idle setting is too lean: Turn the low speed screw (L) counterclockwise until the engine runs and accelerates smoothly. It is usually necessary to change the setting of the idle speed screw (LA) after every correction to the low speed screw (L). English Fine tuning for operation at high altitude A slight correction of the setting may be necessary if engine does not run satisfactorily: N Turn high speed screw (H) clockwise (leaner) - no further than stop. If the setting is too lean there is a risk of engine damage due to insufficient lubrication and overheating. MS 271, MS 291, MS 291 C 41

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MS 271, MS 291, MS 291 C
English
41
General Information
The carburetor comes from the factory
with a standard setting.
This setting provides an optimum fuel-air
mixture under most operating
conditions.
With this carburetor it is only possible to
correct the adjusting screws within fine
limits.
Standard Setting
N
Stopping the engine
N
Check the air filter and clean or
replace if necessary.
N
Check the spark arresting screen
(country-specific) in the muffler and
clean or replace if necessary.
N
Turn the high speed screw (H)
counterclockwise as far as stop (no
more than 3/4 turn).
N
Turn the low speed screw (L)
carefully clockwise as far as stop,
then turn it back 1 full turn.
Readjust idle
Engine stops while idling
N
Open the low speed screw (L) one
full turn.
N
Turn the idle speed screw (LA)
clockwise until the chain begins to
run – then back it off 1 full turn.
Chain runs when engine is idling
N
Open the low speed screw (L) one
full turn.
N
Turn the idle speed screw (LA)
counterclockwise until the chain
begins to run – then turn it another
1 turn in the same direction.
Erratic idling behavior, poor
acceleration (even though low speed
screw is open one turn)
N
Idle setting is too lean: Turn the low
speed screw (L) counterclockwise
until the engine runs and
accelerates smoothly.
It is usually necessary to change the
setting of the idle speed screw (LA) after
every correction to the low speed
screw (L).
Fine tuning for operation at high
altitude
A slight correction of the setting may be
necessary if engine does not run
satisfactorily:
N
Turn high speed screw (H)
clockwise (leaner) – no further than
stop.
Adjusting the Carburetor
If the setting is too lean there is a
risk of engine damage due to
insufficient lubrication and
overheating.
L
5902BA012 KN
LA
H
If the chain continues moving
when the engine is idling, have
your saw checked and repaired by
your servicing dealer.
If the setting is too lean there is a
risk of engine damage due to
insufficient lubrication and
overheating.