Stihl 020 T Service Manual page 30

Checking the spark plug:
Accurate checking of the spark plug
is only possible with a special spark
plug tester.
A provisional check can be carried
out by fitting a clean spark plug in the
spark plug terminal and holding it
against ground. There should be a
powerful sparkover at the electrodes
when the engine is cranked by pulling
the starter rope.
The appearance of the spark plug's insulator nose gives valuable information with regard to the effects of various
operating conditions:
Condition of insulator nose
Normal:
Sooted:
Smeared with oil:
Overheated:
STIHL 020 T
Warning: Do not touch any live
parts - contact with high voltage
can cause serious or fatal
accidents.
Note: It is best to fit a new spark
plug in all cases of doubt.
If there is no sparkover even
though the spark plug is in good
condition, first check the
connections.
Grayish yellow to brown, dry
Velvet-like, dull black
coating of soot
Coating of damp oil carbon
and soot
Welding beads on insulator
nose, pitted electrodes
Note: Chafed insulation on the
ignition lead or short circuit wire will
cause a short-circuit to ground. In this
case the engine with either not start
or only run erratically.
To install the spark plug:
Clean the spark plug seat and
inspect the sealing ring to make
sure it is in good condition.
Fit the spark plug and tighten it
down to 25 Nm (18.5 Ibf.ft).
Meaning
Engine in order;
correct spark plug
(heat range as specified)
Mixture too rich, lack of air
(dirty air filter, choke shutter
partly closed), electrode gap
too wide, wrong spark plug
(heat range too high)
Too much oil in fuel mix
Mixture too lean, spark plug
loose, wrong spark plug (heat
range too low)
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