After thinking about this a little more I am begining to suspect the heat is cooking the Nitro out of my fuel... It seems to affect only my 4 strokes... I have a bunch of Irvine .53 two strokes that don't seem to be affected at all... The Irvines run fine on 0 Nitro.. The 4 strokes appreciate the 15 percent I usually give them... Guess I will start again with a fresh can of fuel and wrap a white towel around it or something...