Sometimes a little piece of hard carbon can get stuck between the electrodes of a sparkplug. Dirt entering the combustion chamber can cause one to form also. Fairly common on yard equipment, chain saws, and motorcycles used in very dusty, dirty conditions. Especially when operated without air cleaners. Not so common in automobiles, but never say never..... I think my babying the big 400 probably caused it. Mixture might be a little too rich as well.
Last edited by capnduane; 12/31/2013 3:06 AM.
