Honda HT-R3811 Owner's Manual page 45

6. Thread the plug in by hand to prevent cross threading.
7. After a new spark plug has been seated by hand, it should be tightened l/2
turn with a wrench to compress its washer.
If a used plug is being reinstalled, it should only require l/8 to l/4 turn
after being seated.
CAUTION:
l
The spark plug must be securely tightened. An improperly tightened plug
can become very hot and possibly damage the engine.
l
Never use a spark plug with an improper heat range.
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