Checking Spark Plug - Stihl 9 Instruction Manual

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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.
If engine is down on power, difficult to
start or runs poorly at idling speed,
first check the spark plug.
•
Remove spark plug –
see chapter "Starting":
•
Clean dirty spark plug.
•
Check electrode gap –
it should be 0.5mm/0.02" $ –
readjust if necessary.

•
Use only resistor type spark plugs
of the approved range.
Rectify problems which have caused
fouling of spark plug:
Incorrect carburetor setting, too much oil
in fuel mix, dirty air filter,
unfavorable running conditions, e.g.
operating at part load.
•
Fit a new spark plug after
approx. 100 operating hours –
or earlier if the electrodes are
badly eroded.
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To reduce the risk of fire and burn injury,
use only spark plugs authorized by
STIHL (see "Specifications"). Always
press spark plug boot  snugly onto
spark plug terminal  of the proper
size. (Note: If terminal has detachable
SAE adapter nut, it must be attached.)
A loose connection between spark plug
terminal and ignition wire connector in
the boot may create arcing that could
ignite combustible fumes and cause a
fire.
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