More Power

If that engine is new, he needs to break it in before any tuning is done. Will fight the tuning during break in process. Warm it up, retorque every bolt that requires a specific torque,,, (head, manifolds etc etc) then put about 10-15 working hours on it. After that, run a compression test, and go from there. Everything Jan said for parts is right on the money! Makes a fun tractor out of it that can do work or play! JMHO, ChadS

As for extra power, loosen your generator or alternator belt before pulling, use a dry element air cleaner instead of the oil-bath, use a straight pipe instead of a muffler, make sure your governor is working correctly and set at the maximum rpm allowed. If you used over-sized pistons you might need to drill out the main jet and load tube to get the right fuel mixture. You could also try larger venturis in the carb.

Really, most of us settle for running. Some of us are pretty fussy and expect running without burning oil. The real connoisseurs among us expect stock horsepower.

There's not much you can do for more power out of that tractor without tearing the engine down again. You should've asked for tips BEFORE spending all that money to rebuild the engine.