poorly tuned EFI is just as bad as poorly tuned carbs and dissies.

I'll ask again. have you done anything to control the mechanical ignition advance?

fuel being burnt around the rings? aren't the rings designed to be the barrier of the combustion process? There is always fuel/air mixture around the rings - that's what they (compession rings) are for - to hold the explosion (burning fuel) and extreme pressues above them so they can be converted into useful work on the top of the piston...

if it was in any way caused by fuel being burnt around (ie past) the rings, there would be lots of scoring on the piston skirts where the oil was burnt off them...