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Figure 8-10. Normal.
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 8-11. Carbon Fouled.
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
Figure 8-12. Worn.
Worn: On a worn plug, the center electrode will
be rounded and the gap will be eroded .010" or
more beyond the correct gap. Replace a worn
spark plug.
Figure 8-13. Wet Fouled.
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 warmup. Oil in the com-
bustion chamber is usually the result of worn pis-
ton rings and/or valve guides.
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