Spark Plug: Inspection

Check the electrodes and inner and outer ceramic insulator of plugs, noting the type of deposits and the degree of electrode erosion.

Fig 1: Checking Electrodes

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1. Normal:

   Brown to grayish-tan deposits and slight electrode wear indicate correct spark plug heat range.

   Fig 2: Identifying Spark Plug Electrode (Normal)

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2. Carbon fouled:

   Dry fluffy carbon deposits on insulator and electrode are mostly caused by slow speed driving in the city, weak ignition, too rich fuel mixture, dirty air cleaner, etc.

   Fig 3: Identifying Spark Plug Electrode (Carbon Fouled)

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3. Oil fouled:

   Wet black deposits show excessive oil entrance into combustion chamber through worn rings and pistons or excessive clearance between valve guides and stems.

   Fig 4: Identifying Spark Plug Electrode (Oil Fouled)

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4. Overheating:

   White or light gray insulator with black or brown spots and bluish burnt electrodes indicate engine overheating. Moreover, the appearance results from incorrect ignition timing, loose spark plugs, wrong selection of fuel, hotter range plug, etc.

   Fig 5: Identifying Spark Plug Electrode (Overheating)

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   CAUTION: Avoid using a plug cleaner because of the spark plug with a platinum tip.