Yamaha YFM25RX Owner's Manual page 90

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1. Spark plug wrench
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To check the spark plug
1. Check that the porcelain insulator around the
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center electrode of the spark plug is a medi-
um-to-light tan (the ideal color when the ATV
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is ridden normally).
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NOTE:
If the spark plug shows a distinctly different color,
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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
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Specified spark plug:
To install the spark plug
1. Measure the spark plug gap with a wire thick-
Spark plug gap:
1. Spark plug cap
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replace it if necessary.
NGK/DR7EA
ness gauge and, if necessary, adjust the gap
to specification.
0.6–0.7 mm (0.024–0.028 in)