Loosen the chassis up so it doesn't push at all and is just to the loose side beginning with corner entry. If you push at all especially going into the corner you will use up a lot of power. Alignment will eat power also-front and rear.
Keep in mind that "stock" classes still have a lot of room for a good builder to make power. I have built engines for the pure stock class that were around 3500$-that one won 22 of its first 24 races and has been torn down repeatedly. A decent set of stock legal heads could easily break 1k$. A good carb can be worth 20hp+ over one that seems to work good. The right cam makes a world of difference.
Common errors are too much piston to head clearance. Bad hone jobs and cheap rings. Poor valve jobs. Wrong cam. Carb with bad mixture curve.