Spark Plug: Inspection

1. Normal:

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

   Fig 2: Checking Spark Plug Electrode (Normal)

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2. Carbon fouled:

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

   Fig 3: Checking Spark Plug Electrode (Carbon Fouled)

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3. Oil fouled:

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

   Fig 4: Checking Spark Plug (Oil Fouled)

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4. Overheating:

   A white or light gray insulator with black or brown spots and bluish burnt electrodes indicate engine overheating, wrong selection of fuel, or loose spark plugs.

   Fig 5: Checking Spark Plug (Overheating)

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Spark plug gap L: 

Standard 

1.0 - 1.1 mm (0.039 - 0.043 in) 

Fig 6: Identifying Spark Plug Gap

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