Checking The Spark Plug - Stihl FS 90 Instruction Manual

English / USA
: Remove the screw (4).
: Lift spark arresting screen (5) and
pull it out.
: Clean spark arresting screen if
necessary – if screen is damaged or
coked up, fit a new one.
: Refit the spark arresting screen.
: Insert screw and tighten down.
: Fit the shroud.
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Checking the Spark Plug

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 as described
in chapter "Starting / Stopping the
Engine".
: Clean dirty spark plug.
: Check the electrode gap (A) and
readjust if necessary – see
"Specifications".
: 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.
Fit a new spark plug after approx.
100 operating hours
or earlier if the electrodes are badly
eroded.
FS 90, FS 90 R