Yamaha BIG BEAR 400 Owner's Manual page 102

1. Spark plug wrench
To check the spark plug
1. Check that the porcelain insulator around the
center electrode of the spark plug is a medi-
8
um-to-light tan (the ideal color when the ATV
is ridden normally).
NOTE:
If the spark plug shows a distinctly different color,
the engine could be operating improperly. Do not
attempt to diagnose such problems yourself. In-
stead, have a Yamaha dealer check the ATV.
2. Check the spark plug for electrode erosion
and excessive carbon or other deposits, and
replace it if necessary.
Specified spark plug:
NGK/DR8EA
To install the spark plug
1. Measure the spark plug gap with a wire thick-
ness gauge and, if necessary, adjust the gap
to specification.
Spark plug gap:
0.6–0.7 mm (0.024–0.028 in)
1. Spark plug gap
2. Clean the surface of the spark plug gasket
and its mating surface, and then wipe off any
grime from the spark plug threads.
8-10