Honda HS521 Owner's Manual page 27

5. Measure the plug gap with a feeler gauge.
0.7
to 0.8 mm (0.027-0.031 in)
Correct as necessary by bending the side electrode.
PLUG GAP
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 com-
press 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 plugs or equivalent. Spark plugs
which have an improper reach or 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.
26