Honda TRX 250EX 2008 Owner's Manual page 122

Spark Plug
7. With the plug washer attached, thread the spark plug in by hand to
prevent cross-threading.
Tighten the spark plug:
If the old plug is good:
1/8 turn after it seats.
If installing a new plug, tighten it twice to prevent loosening:
a) First, tighten the plug:
NGK:
DENSO:
b) Then loosen the plug.
c) Next, tighten the plug again:
1/8 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.
8. Reinstall the spark plug cap. Take care to avoid pinching any cables
or wires.
Servicing Your Honda
114
3/4 turn after it seats.
1/2 turn after it seats.