I think you have hit upon the fix. RC engines are designed to have muffler pressure and often the venturi is too bog to work without it. This is especially true with a light plane that accelerates quickly. One fix is to get the fuel pickup inboard, at least even with the venturi. The other is to choke down the venturi.
Finally, some (maybe all) contests allow you to just use the muffler with muffler pressure. The weight and back pressure of the muffler is a tradeoff for getting the engine to run.
Or you could just dump 75 amps through a 40,000 RPM dentist's drill and forget about it.