Or trade up to bigger tractor. Why do people want to abuse these little tractors anyhow? First they ask "what is the largest_ _ _ _ _ can I use on my,,,,,,,,,,,,,,," then they want to know how to squeeze more horsepower from their engine. In the end they wonder why there's coolant in oil pan and exhaust is like a whistling tea kettle spout.ain't gonna get much more out of it until you can get more air into it.
you can turn the pump up a little but you might be wise to put a pyrometer on it, and keep a close eye.