Plugs look good, but piston ring is fried... What gives?

[IDoSeaDoo]

So I've been running this boat for about 22 hours after rebuilding top end, and the front cylinder has always been 100F hotter than the rear. The temps were in the high 1000's to low 1100's. I had to tear it down recently when I found that my base gasket was failing and found that my MAG cylinder's piston ring was out of spec. The ring-end gap was about 1.2mm. Now since it was already running hot, I had adjusted the high speed screw on it out about 1/2 turn, dropping the temps somewhat. This was evident in the plug, which was a darker chocolate brown. IMO, the plug was not looking lean, yet my rings are toast anyway. Can anyone hint to me why?

 

[Albysure]

I thought if you had chocolate colored plugs your mixture was good... Lean I thought was a white color...are you premixing or are you still using the oil system?....how hard did you ride it after rebuild?

 

[Dr Honda]

It's not allways easy to read a plug on a 2-stroke. (depending on oil mix, and how it's ridden) personally... I like the plugs dark.


Post a picture of the piston crown. That will tell me how it was running.