Did you get to try the original gearing to see how it did? It may be possible the engine was sluggish before due to carb/spark issues, but it seems like it was very sluggish before if that's the case. Does your Mychron 4 (if I remember right?) retain the highest RPM? Just a thought to verify it's actually hitting rev-limit or having fuel/spark issues. The 47 second lap is 2 seconds quicker than your previous best right?
