Spark Plug - Stihl MS 171 Instruction Manual

25 Spark Plug

24.3 Standard Setting
H L
► Turn high speed screw (H) counterclockwise
as far as stop (no more than 3/4 turn).
► Turn the low speed screw (L) clockwise as far
as stop, then turn it back 1/4 turn.
24.4 Adjusting Idle Speed
► Carry out the standard setting.
► Start and warm up the engine.
L
LA
24.4.1 Engine stops while idling
► Turn the idle speed screw (LA) clockwise until
the chain begins to run – then back it off
2 turns.
24.4.2 Saw chain runs while engine is idling
► Turn the idle speed screw (LA) counterclock‐
wise until the chain stops moving – then turn it
another 2 turns 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.
24.4.3 Erratic idling behavior, poor accelera‐
tion (even though standard setting of
low speed screw is correct)
Idle setting is too lean
► Turn the low speed screw (L) carefully coun‐
terclockwise, no further than stop, until the
engine runs smoothly and accelerates well.
0458-533-0121-E
It is usually necessary to change the setting of
the idle speed screw (LA) after every correction
to the low speed screw (L).
24.5 Fine Tuning for Operation at
High Altitude
A slight correction of the setting may be neces‐
sary if the engine does not run satisfactorily:
► Carry out the standard setting.
► Warm up the engine.
► Turn high speed screw (H) slightly clockwise
(leaner) – no further than stop.
NOTICE
After returning from high altitude, reset the car‐
buretor to the standard setting.
If the setting is too lean there is a risk of engine
damage due to insufficient lubrication and over‐
heating.
25 Spark Plug
► If the engine is down on power, difficult to start
or runs poorly at idle speed, first check the
spark plug.
► Fit a new spark plug after about 100 operating
hours – or sooner if the electrodes are badly
eroded. Install only suppressed spark plugs of
the type approved by STIHL – see "Specifica‐
tions".
25.1 Removing the spark plug
► Remove the shroud – see "Shroud".
► Pull off the spark plug boot.
► Unscrew the spark plug.
English
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