Checking The Spark Plug - Stihl FS 40 Instruction Manual

Cutting attachment rotates when
engine is idling
N Turn the idle speed screw (LA)
counterclockwise until the tool stops
moving and then turn the screw
another full turn in the same
direction.
If the cutting tool continues to
rotate when the engine is idling,
have your machine checked and
repaired by your servicing dealer.
Erratic idling behavior, engine stops
even though setting of LA-screw has
been corrected, poor acceleration
Idle setting is too lean
N Turn the low speed screw (L)
counterclockwise, no further than
stop, until the engine runs and
accelerates smoothly.
Erratic idling behavior, engine speed
drops when swinging the machine
Idle setting is too rich
N Turn the low speed screw (L)
clockwise (1/8 of a turn or 45° at a
time) until the engine runs smoothly
and accelerates well.
It is usually necessary to change the
setting of the idle speed screw (LA) after
corrections to the low speed screw (L).
FS 40, FS 40 C, FS 50, FS 50 C

Checking the Spark Plug

If the engine is down on power, difficult
to start or runs poorly at idle speed, first
check the spark plug.
Removing the Spark Plug
N Shut down the engine.
The spark plug boot (2) is located in the
cap (1).
The cap (1) protects the spark
plug from damage. Do not operate
the power tool without the cap –
replace a damaged cap.
N Pull off the spark plug boot (2)
together with the cap (1).
N Unscrew the spark plug (3).
If the cap becomes detached when you
pull off the spark plug boot, see
"Installing the Spark Plug."
Checking the Spark Plug
1
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.
N Clean dirty spark plug.
N Check the electrode gap (A) and
readjust if necessary – see
"Specifications."
N
Use only resistor type spark plugs of
the approved range.
Rectify problems which have caused
fouling of spark plug:
N Too much oil in fuel mix.
N Dirty air filter.
N Unfavorable running conditions,
e.g. operating at part load.
English
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