23BR 340, BR 340 L, BR 420, BR 420 C
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 – see “Starting /
Stopping the Engine“.
: Clean dirty spark plug.
: Check 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.
To reduce the risk of fire and burn
injury, use only spark plugs
authorized by STIHL. Always press
spark plug boot (2) snugly onto
spark plug terminal (1) of the proper
size. (Note: If terminal has
detachable SAE adapter nut, it must
be attached.)
A loose connection between spark
plug boot and ignition wire
connector in the boot may create
arcing that could ignite combustible
fumes and cause a fire.
If the engine is down on power, check
the spark arresting screen* in the
muffler.
Wait until engine has cooled down
completely before performing the
following operations.
: Use suitable tool to squeeze ends of
clip (1) together and then lift the clip
away.
: Pull the spark arresting screen (2)
out of the muffler.
* see “Guide to Using this Manual”
00BA036 TR
1
Spark Arresting Screen*
in Muffler
373BA031 KN
1
2
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