Honda and WT40X Owner's Manual page 38

SERVICING YOUR HONDA PU,MP
5. Install the spark plug carefully, by hand! to avoid cross-threading.
6.After the spark plug seats, tighten with a 13/'16-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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