Honda WB20XT Guide De L'utilisateur page 30

4. Check that the spark plug washer is in good condition, and thread the spark
plug in by hand to prevent cross-threading.
5. After the spark plug seats, tighten with a 21 mm (13/16-inch) spark plug
wrench to compress the washer.
If reinstalling the used spark plug, tighten 1/8—1/4 turn after the spark plug
seats.
If installing a new spark plug, tighten 1/2 turn after the spark plug seats.
TORQUE: 18 N∙m (1.8 kgf∙m, 13 lbf∙ft)
CAUTION:
The spark plug must be securely tightened. An improperly tightened spark
plug can become very hot and may cause engine damage.
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