Engine Management; Adjusting The Carburetor - Stihl MS 171 Instruction Manual

Engine Management

Exhaust emissions are controlled by the
design of the fundamental engine
parameters and components (e.g.
carburation, ignition, timing and valve or
port timing) without the addition of any
major hardware.
MS 171, MS 181, MS 181 C, MS 211, MS 211 C

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.
Standard setting
N Switch off 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.
L
N Turn 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 turn.
Adjusting idle speed
Engine stops while idling
N Turn the low speed screw (L)
carefully clockwise as far as stop,
then turn it back 1 turn.
N Turn the idle speed screw (LA)
clockwise until the chain begins to
run – then back it off 2 turns.
Chain runs when engine is idling
N Turn the low speed screw (L)
carefully clockwise as far as stop,
then turn it back 1 turn.
N
Turn the idle speed screw (LA)
counterclockwise until the chain
begins to run – then turn it another
2 turns 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 standard
setting of low speed screw is correct)
Idle setting is too lean –
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
English
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