Spark Plug - Stihl MS 391 Safety Manual

English

Spark Plug

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
2
1
N
Loosen screws (1)
N
Remove the shroud (2)
30
N
Pull off the spark plug boot
N
Unscrew spark plug
Checking the spark plug
1
N
Clean dirty spark plug.
N
Check electrode gap (A) and
readjust if necessary – see
"Specifications".
1
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.
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.
Install spark plug
A
N
Screw in the spark plug and press
on the spark plug boot
N
Refit the shroud and tighten the
screws
1
MS 311, MS 391