Kohler Courage SV470 Service Manual page 54

Section 7
Electrical System and Components
Inspection
Inspect the spark plug as soon as it is removed from
the cylinder head. The deposits on the tip are an
indication of the general condition of the piston rings,
valves, and carburetor.
Normal and fouled plugs are shown in the following
photos.
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 regapped and reused.
Worn: On a worn plug, the center electrode will be
rounded and the gap will be eroded .010" or more
than the correct gap. Replace a worn spark plug
immediately.
7.2
Chalky White Deposits: Chalky white colored
deposits indicate overheating. This condition is
usually accompanied by excessive gap erosion. A
clogged grass screen, clogged cooling fins, and lean
carburetion are some causes of overheating.
Carbon Fouled: Soft, sooty, black deposits indicate
incomplete combustion. Incomplete combustion
is usually caused by over-rich carburetion, weak
ignition, or poor compression.
Wet Fouled: A wet plug is caused by excess fuel, or
oil in the combustion chamber. Excess fuel could be
caused by operating the engine with too much choke
or a dirty air filter. Oil in the combustion chamber is
usually caused by worn piston rings or valve guides.