Check the head bolts and make sure they are snug...I had the same problem with MY 'Cane XP and it turned out my head bolts were loose...that will cause a lean condition (excess air entering the combustion chamber where it SHOULDN'T) even though it is SET rich to the point where it shouldn't even run and the abscence of good compression will result in incomplete burn...

Actually you may want to take the head OFF and check the seating surfaces...clean them up real good and use a little high temp RTV gasket sealant when putting it back together because more than likely if the head was loose or not tightened evenly it more than likely warped when it overheated.