Stihl MS 391 Safety Manual

MS 311, MS 391
English
30
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)
N Pull off the spark plug boot
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.
Install spark plug
N Screw in the spark plug and press
on the spark plug boot
N Refit the shroud and tighten the
screws
Spark Plug
1
4903BA002 KN
1
1
2
4903BA007 KN
000BA039 KN
A
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.
1
000BA045 KN
4903BA008 KN

Stihl MS 391 Specifications

General

Motor type	2-stroke motor
Chain gauge	1.6 mm
Chain pitch	3/8 \
Automatic oiling	Yes
Oil tank capacity	0.35 L
Fuel tank capacity	0.6 L
Engine displacement	64.1 cm³
Engine power	4.4 hp
Power source	Gasoline

Weight and Dimensions

Weight	6200 g