Honda EX650 Owner's Manual page 29

6. Check that the spark plug washer is in good condition, and thread the spark
plug in by hand to prevent cross-threading.
7. After the spark plug is seated, tighten with a spark plug wrench to compress
the washer.
-
If installing a new spark plug, tighten l/2 turn after the spark plug seats
to compress the washer. If reinstalling a used spark plug, tighten 1/8-
1/4 turn after the spark plug seats to compress the washer.
piciq
The spark plug must be securely tightened. An improperly
tightened spark plug can become very hot and could damage the
engine.
Never use spark plugs which have an improper heat range. Use only the
recommended spark plugs or equivalent.
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