MS 661
English
34
Correcting the carburettor setting for use
at high altitudes
The setting may have to be marginally
corrected if engine performance is
unsatisfactory at high altitudes:
N Make standard setting
N Let the engine warm up
N Turn the high speed adjusting
screw (H) slightly clockwise (leaner)
– max. up to the stop
NOTICE
After descending from a high altitude,
restore the carburettor setting to the
standard setting.
If you make the setting too lean it will
increase the risk of engine damage
through lack of lubrication and
overheating.
N If the engine is down on power,
difficult to start or runs poorly at idle
speed, first check the spark plug.
N 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
"Specifications".
Removing the spark plug
N Turn the cap above the rear handle
in the direction of the arrow and
remove the filter cover
N Unplug spark plug boot (1)
N Unscrew spark plug
Checking the spark plug
N Clean dirty spark plug.
N Check electrode gap (A) and
readjust if necessary – see
"Specifications".
N Rectify the problems which have
caused fouling of the spark plug.
Possible causes are:
– Too much oil in fuel mix.
– Dirty air filter.
– Unfavorable running conditions.
WARNING
If the spark plug comes with a
detachable adapter nut (1), screw the
adapter onto the thread and tighten it
down firmly to reduce the risk of arcing
and fire.
Spark Plug
1166BA011 AM
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