Yamaha YXR7FD Owner's Manual page 138

Inspection
The spark plug is an important engine compo-
1
nent and is easy to inspect. The condition of
the spark plug can indicate the condition of
the engine.
The ideal color of the porcelain insulator
around the center electrode is a medium-to-
light tan for a vehicle that is being ridden nor-
mally.
You should periodically remove and inspect
1. Spark plug wrench
the spark plug because heat and deposits will
cause the spark plug to slowly break down
and erode. If electrode erosion becomes ex-
cessive, or if carbon and other deposits are
excessive, you should replace the spark plug
with the specified plug.
Specified spark plug:
CPR7EA-9 (NGK)
8-25