my son runs on dirt with a previous asphault car and i debated removing the lowering blocks in the rear , to see if it would improve anything, im having a problem with the engine popping, it revs great it idles great, when you put it on the track it runs great on pace laps but when you drop the hammer it starts popping and wont make it over 4000 rpm, ive checked the fuel psi, floats in carb, power valve, plugs. wires, timing, i just dont know what im missing.