Stihl FC 91 User Manual

FC 91
English
21
If the engine is down on power, difficult
to start or runs poorly at idling speed,
first check the spark plug.
Install a new spark plug after approx.
100 operating hours or earlier if the
electrodes are badly eroded/corroded.
The wrong fuel mix (too much engine oil
in the gasoline), a dirty air filter and
unfavorable running conditions (mostly
at part throttle etc.) affect the condition
of the spark plug. These factors cause
deposits to form on the insulator nose
which may degrade performance.
Removing the Spark Plug
N Remove the cover (1).
N Pull off the spark plug boot (2).
N Unscrew the spark plug (3).
Checking the Spark Plug
N Clean dirty spark plug.
N Check electrode gap (A) and
readjust if necessary – see chapter
"Specifications."
N Use only resistor type spark plugs of
the approved range.
Rectify problems which have caused
fouling of spark plug:
– too much oil in fuel mix,
– dirty air filter,
– unfavorable running conditions, e.g.
operating at part load.
WARNING
To reduce the risk of fire and burn injury,
use only spark plugs authorized by
STIHL. Always press the spark plug
boot (1) snugly onto the spark plug
terminal (2).
Do not use a spark plug with a
detachable SAE adapter terminal (3).
Arcing may occur that could ignite
combustible fumes and cause a fire.
This can result in serious injuries or
damage to property.
N Only use resistor type spark plugs
with solid, non-threaded terminals
Installing the Spark Plug
N Screw the spark plug (3) into the
cylinder.
N Tighten down the spark plug (3) with
the combination wrench.
Spark Plug
3
2
1
0000-GXX 0537-A0
000BA039 KN
A
2
1
0000-GXX-1831-A0
3

Stihl FC 91 Specifications

General

Brand	Stihl
Model	FC 91
Category	Trimmer
Language	English