Rcpilet, sent you a PM and some information. If you can only use this carb try a 16/8 or 16/6 prop. Your RPM will go to near 7000 I bet. However I think the carb is too big. Also think about the muffler too. The engine is just a little compressor and can only do so much. You can put all kinds of air and fuel to it but if it can't breath and or use all the air and fuel it won't go anywhere. Same thing with over proping. Basically the less load the faster it turns and the more power you will get. All you need to do is find that balance.

Tim