Yamaha GRIZZLY Ultramatic YFM660FP Owner's Manual page 143

Inspection
The spark plug is an important engine compo-
nent and is easy to inspect. The condition of
the spark plug can indicate the condition of
the engine. The ideal color on the white insu-
lator around the center electrode is a medium-
to-light tan color for a ATV that is being ridden
normally. Do not attempt to diagnose such
problems yourself. Instead, take the ATV to a
Yamaha dealer. You should periodically re-
move and inspect the spark plug because
heat and deposits will cause the spark plug to
slowly break down and erode. If electrode
erosion becomes excessive, or if carbon and
other deposits are excessive, you should re-
place the spark plug with the specified plug.
Specified spark plug:
DPR8EA-9 (NGK)
Installation
1. Measure the electrode gap with a wire
thickness gauge and, if necessary, adjust
the gap to specification.
Spark plug gap:
0.8 ~ 0.9 mm (0.031 ~ 0.035 in)
a. Spark plug gap
2. Clean the gasket surface. Wipe off any
grime from the threads.
3. Install the spark plug and tighten it to the
specified torque.
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