What are your temps running?? An air leak could cause this or your carb being all gunct up.. Are you tunning by temp or is that where you put it to get it to run properly??
I was thinking an air leak, too.
Otherwise, maybe poor LSN tune, extreme low humidity, high barometric pressure, very low ambient temps, sea level running, etc. (not likely).
If you have low humidity and low ambient temps ;-it would make a nitro engine a thirsty engine but would hardly require the engine to be richened up more than the factory settings unless you're using a hot tip glowplug or have an airleak at the carb needles/slider......check the fueltank to make sure its holding positive pressure and choosing the right glowplug is also key to proper tuning....My 3.3 likes and runs its best on Trinity monsterbrew 20% with an OS8 glowplug with the LSN set to 1 3/4 turns out and the HSN set at 3 3/4 - 3 turns out depending on humidity and temps....