Spark Plug - Stihl MS 251 Instruction Manual

English

Spark Plug

If engine is down on power, difficult to
start or runs poorly at idling speed, first
check the spark plug.
Fit a new spark plug after approx. 100
operating hours or earlier if the
electrodes are badly eroded.
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 result in trouble in operation.
Removing the spark plug
Remove the shroud – see "Shroud"
N
Pull off the spark plug boot
N
Unscrew spark plug
N
46
Checking the spark plug
Clean the spark plug if it is dirty
N
Check the electrode gap (A) and
N
readjust if necessary – see
"Specifications"
Use only resistor type spark plugs of
N
the approved range
Correct the problems that have caused
fouling of the spark plug:
too much oil in fuel mix,
–
dirty air filter,
–
unfavorable running conditions, e.g.
–
operating at part throttle.
A
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.
Only use resistor type spark plugs
N
with solid, non-threaded terminals
1
3
2
MS 251, MS 251 C