Spark Plug Inspection - Yamaha Big Bear YFM400R Owner's Manual

EBU01182

Spark plug 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.
For example, a very white center electrode
porcelain color could indicate an intake air
leak or carburetion problem for that cylinder.
Do not attempt to diagnose such problems
yourself.
Instead, take the ATV to a Yamaha dealer.
You should periodically remove and inspect
the spark plug because heat and deposits will
cause the spark plug to slowly break down
and erode. If electrode erosion becomes ex-
cessive, you should replace the spark plug
with one of the proper type.
Standard spark plug:
DR8EA (NGK)
Before installing the spark plug, measure the
electrode gap with a wire thickness gauge
and adjust it to specification.
Spark plug gap:
0.6–0.7 mm (0.024–0.028 in)
a. Spark plug gap
When installing the spark plug, always clean
the gasket surface and its mating surface.
Wipe off any grime from the threads and tight-
en it to the specified torque.
Tightening torque:
Spark plug:
17.5 Nm (1.75 m·kgf, 12.5 ft·lbf)
8-12