To lessen the pinch atr TDC start engine run extremely rich at full thottle never exceding 140 F for 10 tanks then cool motor at TDC. Repeat process 2 times. If done corectly you should have minal pinch if any. If motor is still not to your liking lean out the motor as much as possible cover cooling head with a sock preferably crew or in a pinch a foam dixie cup will do then procede to hold the throttle wide open until motor reaches desired level of performance.
Hope this helps.