I'm sure you do not bigger fuel lines. These things just sip gas ( I have one ). I did have the same problem with another brand of engine and tracked it down to the battery. It would supply enough voltage when running static but as soon as the prop unloaded it started backfiring & missing. I was running an 1100 mah nimh and switched to a 1400 mah nicad - end of problem. This may or maynot help.