Instruction Manual

MS 311, MS 391
English
34
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 Carry out the standard setting.
N Warm up the engine.
N Turn high speed screw (H) slightly
clockwise (leaner) – no further than
stop.
NOTICE
After returning from high altitude, reset
the carburetor to the standard setting.
If the setting is too lean there is a risk of
engine damage due to insufficient
lubrication and overheating.
N If engine performance deteriorates,
check the spark arresting screen in
the muffler
N Let the muffler cool down
N Unscrew the screw (1)
N Pull out spark arresting screen (2)
N Clean the dirty spark arresting
screen, replace if damaged or
heavily carbonized
N Refit the spark arresting screen
N Fit screw
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".
Remove the spark plug
N Move the Master Control lever to the
stop position 0
N Push the hand guard forwards – the
saw chain is blocked
N Loosen screws (1)
N Remove the shroud (2)
Spark Arresting Screen in
Muffler
0001BA009 KN
2
1
Spark Plug
1
4903BA002 KN
1
1
2