Hi! I checked my 493 cui stroker with a endoscope through the spark plug holes and all 8 cylinders looked nice, it was only in one cylinder i see some black marks, same carbone dust. What can it be? Is it maybe a sharp edge on a ring or something so it builds up little carbon? The engine has go 400 problem free miles after cam break in and stands for a few mounth now in off season, i drag the engine around by hand a little now and check all cylinders with a endoscope. Is this something to care about? I send the pictures to a well known engine builder here in Sweden and he says it look fine, probably a sharp edge on a ring or something like that.