Kohler Courage SV710-740 Service Manual page 58

Normal: A plug taken from an engine operating under
normal conditions will have light tan or gray colored
deposits. If the center electrode is not worn, a plug
in this condition could be set to the proper gap and
reused.
Carbon Fouled: Soft, sooty, black deposits indicate
incomplete combustion caused by a restricted air
cleaner, over-rich fuel mixture, weak ignition, or poor
compression.
Worn: On a worn plug, the center electrode will be
rounded and the gap will be greater than the specified
gap. Replace a worn spark plug immediately.
Wet Fouled: A wet plug is caused by excess fuel or
oil in the combustion chamber. Excess fuel could
be caused by a restricted air cleaner, a carburetor
problem, or operating the engine with too much
choke. Oil in the combustion chamber is usually
caused by a restricted air cleaner, a breather problem,
or worn piston rings, cylinder walls or valve guides.
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.