Yamaha XZ550RJ 1982 Owner's Manual page 161

Spark plug inspection
The spark plug is an important engine com-
ponent and is easy to inspect. The condition
of the spark plug can indicate something of
the condition of the engine.
For example, a very white center electrode
porcelain color could indicate an intake tract
air leak or carburetion problem for that
cylinder. Do not attempt to diagnose such
problems yourself. Instead, take the motor-
cycle to your Yamaha dealer.
You should periodically remove and inspect
the spark plug because heat and deposits will
cause any spark plug to slowly break down
and erode. If electrode erosion becomes ex-
cessive, or if carbon and other deposits are
excessive, you should replace the spark plug
with one of the proper types.
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