Honda HP400 Owner's Manual page 40

5. Measure the plug gap with a feeler gauge.
Correct as necessary by bending the side electrode.
The gap should be:
0.70 - 0.80 mm (0.028 -
0.031 in)
PLUG GAP:
0.7 - 0.8 mm
10.028 - 0.031 in)
SIDE ELECTRODE
6. Make sure 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.
NOTE:
If installing a new spark plug, tighten l/2 turn after the spark plug seats to
compress the washer. If reinstalling
a used spark plug, tighten l/8 to l/4 turn
after the spark plug seats.
l
Use only the recommended spark plug or equivalent. Spark plug
which have an improper heat range may cause engine damage.
l
The spark plug must be securely tightened. An improperly tightened
spark plug can become very hot and may damage the engine.
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