【8-4】
APPENDIX
Spark Plug:
The spark plug ignites the fuel and air mixture in the combustion
chamber. To do this effectively and at the proper time, the correct
spark plug must be kept clean and the gap adjusted.
Tests have shown the plug listed in the General Information chapter
to be the best plug for general use.
Since spark plug requirements change with the ignition and
carburetion adjustments and with riding conditions, whether or not
a spark plug of the correct heat range is used should be determined
by removing and inspecting the plug.
Terminal [A] Insulator [B]
Gasket [C] Center Electrode [D]
Gap [E] (0.8~0.9 mm) Reach [F]
Side Electrode [G]
When a plug of the correct heat range is being used, the electrodes
will stay hot enough to keep all the carbon burned off, but cool
enough to keep from damaging the engine and the plug itself. This
temperature is about 400 ~ 800
o
C(750 ~ 1,450
o
F) and can be judged
by noting the condition and color of the ceramic insulator around
the center electrode.
If the ceramic is clean and of a light of a light brown color, the plug
is operating at the right temperature.
A spark plug for higher operating temperatures sometimes may be
needed for severe conditions, such as continuous high-speed riding,
or towing heavy loads. Such a plug is designed for better cooling
efficiency so that it will not overheat and thus is often called a
“colder” plug. If a spark plug with a heat range is used – that is, a
“cold” plug that cools itself too well, - the plug will stay too cool to
burn off the carbon, and the carbon will collect on the electrodes
and the ceramic insulator.
The carbon on the electrodes conducts electricity, and can short the
center electrode to ground by either coating the ceramic insulator or
bring across the gap. Such a short will prevent an effective spark.
Carbon build-up on the plug can also cause other troubles. It can
heat up red-hot and cause pre-ignition and knocking, which may
eventually burn a hole in the top of the piston.
Spark Plug Inspection
● Remove the spark plug and inspect the ceramic insulator.
Whether or not the right temperature plug is being used can be
ascertained by noting the condition of the ceramic insulator around
the electrode. A light brown color indicates the correct plug is being
used. If the ceramic is black, it indicates that the plug is firing at too
low a temperature, so the next hotter type should be used instead.
If the ceramic is white, the plug is operating at too high a
temperature and it should be replaced with the next colder type.
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