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Spark Plugs Tell A Story

Normal Spark Plug
The porcelain should be a light tan or gray.

Carbon Fouled Plug
Has soft, black, sooty deposits indicating an improperly tuned engine.

Worn Out Spark Plug
This plug has been in the engine too long. Note the large gap and worn out center electrode. This plug can misfire and cause stumbling and loss of power.

Oil Fouled Plug
Has wet-looking, black deposits indicating bad rings or valve seals.

Heavily Damaged Spark Plug
Indicates possible detonation. Cylinder should be watched between services. Not only can the plug be damaged, but the engine as well.

Bridged or Almost Bridged Spark Plug
Caused by excessive carbon or oil build up on the spark plug. When the gap is bridged, the cylinder goes dead.
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