Compression sounds fine for not being run to seat the rings yet.
Once your ready to try again spritz a little premix direct into the carb and get a helper to do a good 2nd gear push start as fast as you can down a long stretch.
I doubt this is possible, but are both the piston and the carb slide in facing the right direction ? I think the piston would have caught the ring ends in a port possibly, and the only way the carb slide could be backwards is if it had pin grooves on both sides.
Again I gotta stress, you need to be absolutely certain your exhaust isnt plugged, even partially, have seen this same symptom dozens of times on sleds, only to find a mouse nest deep inside the pipe, out of sight.