In terms of fuel, I broke it in using 20% castor and 80% oil. I have tried different nitro percentages and nothing really makes a difference.I forgot to mention that this engine can only be stopped when it runs out of fuel.It is amazing to see the carby barrel fully shut and the damn thing still keeps going! from what the other comments say, I suspect that there is a massive air leak somewhere.My next course of action is to try a carby from a sweet running Thunder tiger .61 I have.I've used gasket paste to seal the backplate and have checked all bolts and looked for flashing. If the new carby finally cures the beast, then I will fork out for a Perry carb.