Honda EG2500X Owner's Manual page 40

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
1/2 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.
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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