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GAP BRIDGED
IDENTIFIED BY DEPOSIT BUILDUP CLOSING GAP BETWEEN ELECTRODES.
CAUSED BY OIL OR CARBON FOULING. REPLACE PLUG, OR, IF DEPOSITS ARE NOT
EXCESSIVE, THE PLUG CAN BE CLEANED.
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OIL FOULED
IDENTIFIED BY WET BLACK DEPOSITS ON
THE INSULATOR SHELL BORE ELECTRODES.
CAUSED BY EXCESSIVE OIL ENTERING COMBUSTION CHAMBER THROUGH WORN RINGS AND
PISTONS, EXCESSIVE CLEARANCE BETWEEN VALVE GUIDES AND STEMS, OR WORN OR LOOSE
BEARINGS. CORRECT OIL PROBLEM AND REPLACE THE PLUG.
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CARBON FOULED
IDENTIFIED BY BLACK, DRY FLUFFY CARBON DEPOSITS ON INSULATOR TIPS. EXPOSED
SHELL SURFACES AND ELECTRODES.
CAUSED BY TOO COLD A PLUG, WEAK IGNITION, DIRTY AIR CLEANER, DEFECTIVE FUEL
PUMP, TOO RICH A FUEL MIXTURE, IMPROPERLY OPERATING HEAT RISER OR EXCESSIVE
IDLING. CAN BE CLEANED.
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PRE-IGNITION
IDENTIFIED BY MELTED ELECTRODES AND POSSIBLY BLISTERED INSULATOR. METALLIC
DEPOSITS ON INSULATOR INDICATE ENGINE DAMAGE.
CAUSED BY WRONG TYPE OF FUEL, INCORRECT IGNITION TIMING OR ADVANCE, TOO HOT A
PLUG, BURNT VALVES OR ENGINE OVERHEATING. REPLACE THE PLUG.
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OVERHEATING
IDENTIFIED BY A WHITE OR LIGHT GRAY INSULATOR WITH SMALL WHITE OR GRAY BROWN
SPOTS AND WITH BLUISH BURNT APPEARANCE OF ELECTRODES.
CAUSED BY ENGINE OVERHEATING, WRONG TYPE OF FUEL, LOOSE SPARK PLUGS, TOO HOT
A PLUG, LOW FUEL PUMP PRESSURE OR INCORRECT IGNITION TIMING. REPLACE THE
PLUG.
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FUSED SPOT DEPOSIT
IDENTIFIED BY MELTED OR SPOTTY DEPOSITS RESEMBLING BUBBLES OR BLISTERS.
CAUSED BY SUDDEN ACCELERATION. CAN BE CLEANED IF NOT EXCESSIVE. 0THERWISE
REPLACE PLUG.
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