Kohler K91 Service Manual page 78

Figure
8-1 0.
Normal:
A plug taken from an engine operating
under normal conditions will have light tan or gray
deposits. If the center electrode is not worn . a
plug in this condition may be gapped and re-used .
Figure
8-1 1 .
Carbon Fouled:
Soft . sooty. black deposits indi­
cate incomplete combustion . This is usually
caused by overrich carburetor settings . weak igni­
tion or poor compression .
8 . 8
Normal.
Carbon Fouled.
Figure
8-1 2 .
Worn :
On a worn plug . the center electrode will
be rounded and the gap will be eroded . 0 1 0 " or
more beyond the correct gap . Replace a worn
spark plug .
Figure
8-1 3 .
Wet Fouled:
Wetness is caused by excess fuel or
oil in the combustion chamber. Excess fuel could
be caused by operating the engine without fully
opening the choke after warmu p . Oil in the com­
bustion chamber is usually the result of worn pis­
ton rings and/or valve guides.
Worn.
Wet Fouled.