Checking The Spark Plug - Stihl BT 121 Manual De Instrucciones

Erratic idling behavior, poor
acceleration
: Carry out standard setting with the
low speed screw (L).
Idle setting too lean:
: Turn the low speed screw (L)
counterclockwise until the engine
runs and accelerates smoothly.
It is usually necessary to change the
setting of the idle speed screw (LA)
after every correction to the low speed
screw (L).
Fine tuning the carburetor for
operation at high altitude
A slight correction may be necessary if
the engine does not run satisfactorily:
: Check the standard setting.
: Warm up the engine.
: Turn the high speed screw (H)
clockwise (leaner).
BT 121

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.
English / USA
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.
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