Inspection; Normal; Worn; Carbon Fouled - Kohler CH940-CH1000 Service Manual

Inspection

Inspect each spark plug as it is removed from cylinder head. Deposits on tip are an indication of general condition of
piston rings, valves, and carburetor.
Normal and fouled plugs are shown in following photos:

Normal

A plug taken from an engine
operating under normal conditions
will have light tan or gray colored
deposits. If center electrode is not
worn, a plug in this condition could
be set to proper gap and reused.
Wet Fouled
A wet plug is caused by excess
fuel or oil in combustion chamber.
Excess fuel could be caused by a
restricted air cleaner, a carburetor
problem, or operating engine with
too much choke. Oil in combustion
chamber is usually caused by a
restricted air cleaner, a breather
problem, worn piston rings, or valve
guides.
62 690 01 Rev. C

Worn

On a worn plug, center electrode will
be rounded and gap will be greater
than specifi ed gap. Replace a worn
spark plug immediately.
Overheated
Chalky, white deposits indicate very
high combustion temperatures. This
condition is usually accompanied
by excessive gap erosion. Lean
carburetor settings, an intake air
leak, or incorrect spark timing are
normal causes for high combustion
temperatures.
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Carbon Fouled

Soft, sooty, black deposits indicate
incomplete combustion caused by
a restricted air cleaner, over rich
carburetion, weak ignition, or poor
compression.
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