Subaru Legacy 2005 Service Manual page 1692

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2) Carbon fouled:

Dry fluffy carbon deposits on insulator and elec-

trode are mostly caused by slow speed driving in

the city, weak ignition, too rich fuel mixture, dirty air

cleaner, etc.

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.

4) Overheating:

White or light gray insulator with black or brown

spots and bluish burnt electrodes indicate engine

overheating. Moreover, those appearance also re-

sults from incorrect ignition timing, loose spark

plugs, wrong selection of fuel, etc.

D: ADJUSTMENT

Clean the spark plugs using a wire brush.

Clean and remove the carbon or oxide deposits.

But do not wear away ceramic insulator at this time.

If deposits are too stubborn, replace the spark

After cleaning the spark plugs, correct the spark

plug gap using a gap gauge.

Do not use a plug cleaner because the spark plugs

are applied with iridium tip.

Spark plug gap L:

0.7 — 0.8 mm (0.028 — 0.031 in)

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