Slap some BMX pedals on the rear axle for tucking, and getting your knee down.
Mix up some Nitro remote control car fuel into your fuel mix(start with 20%)see how she goes then.
Are the holes for the air to pass through on both sides of the carby, nice and open? Same with the exhaust pipe where it connects to the motor. What's in the muffler? If you pull on the throttle cable outer,(away from carby), can you make it rev harder than the throttle will let you? Or turf the motor, use the running gear, and slap a big chainsaw motor in there.
Wear all black, and get a rice paddy big round straw hat.
Nice job of making something not real cool, look cool