Lowering the sleeve sometimes give you a renewed pinch at TDC. That is if you still got a shim under it now.

Rather than replace the Piston and Sleeve, my suggestion would be to sell the engine to someone getting into racing as a starter engine. You can sell used Nelsons pretty easily for $150. Take that, plus the $150 it would have cost you for a new piston / sleeve and buy a new engine.

I have been very impressed with my latest two Nelsons. Not sure if it is the minor changes that were made in the carb and crank areas or what, but they sure seem to run better than my older nelsons.