Honda GX25NTT3 Owner's Manual page 35

SERVICING YOUR HONDA ENGINE
6. After the spark plug seats, tighten with a 5/8-inch spark plug wrench
to compress the washer.
If reinstalling the used spark plug, tighten l/8-1/4 turn after the
spark plug seats.
If installing a new spark plug, tighten l/2 turn after the spark plug
seats.
A loose spark plug can overheat and damage the engine.
Over-tightening the spark plug can damage the threads in the
cylinder head.
7. Attach the spark plug cap.
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