Lean condition/ Too Much Heat
Well after reading your conditions, I feel you had a lean condition and way too much heat. First off you said it was 55 degrees, no way can that cooling system adequately cool at those temperatures for very long periods of time. You said hard pulls and then backing off throttle for a while. Hard pulls create high amounts of heat, especially if its already lean on efi. So with the hard pulls,and 55 degrees and deep snow which pulls harder also. I think you just burnt it down from being way too hot outside and inside temperatures plus being lean on fuel due to electronic fuel injection sensing the outside weather conditions. low altitude and those conditions need more fuel. You dont even show any piston wash paterns on top of pistons, lean to read you pistons and plugs, or you will do this again. Heat kills 2 strokes. hope this helps. these are only my thoughts.
