I know someone with a Razzle he tried to put a 61 in it and has the same problems i think his problem is that the engine is upside down in the Razzle. Try turning the engine up the other way or try smaller fuel tube because i think the problem is it is getting to much fuel causing it to flood.
I get the same problem with my pc9 after flying it i alway take the fuel pipe of the carb so the fuel stops get through to it.
Mark ;-)