Honda CRF250F Owner's Manual Installation And Operation page 188

4. Visually inspect the spark plug
electrodes for wear. The centre electrode
(4) should have square edges and the
side electrode (5) should not be eroded.
5. Discard the spark plug if there is
apparent wear or if the insulator is
cracked or chipped.
6. Check the spark plug gap (6) using a
wire-type feeler gauge. If adjustment is
necessary, bend the side electrode
carefully.
The gap should be:
0.8—0.9 mm (0.03—0.04 in)
(5)
(4)
(4) Centre electrode
(5) Side electrode
(6)
(6) Spark plug gap
7. Make sure the plug washer is in good
condition.
8. With the plug washer attached, thread
the spark plug in by hand to prevent
cross-threading.
9. Tighten the spark plug:
• If the old plug is good:
1/5 turn after it seats.
• If installing a new plug, tighten it twice
to prevent loosening:
a) First, tighten the plug:
1/4 turn after it seats.
b) Then loosen the plug.
c) Next, tighten the plug again:
1/5 turn after it seats.
An improperly tightened spark plug can
damage the engine. If a plug is too loose, a
piston may be damaged. If a plug is too
tight, the threads may be damaged.
10. Reinstall the spark plug cap. Take care
to avoid pinching any cables or wires.
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