Well, definitely no air leak. Tank is hermetically sealed

whodeany99, If I pull the line off the muffler the engine cuts pretty much straight away.

I think I'm just going to have to go and change the engine round.

It's a real shame as I think it totally spoils the look of what is a very pretty airplane. Least you can't notice it when she's flying and that's the main thing, to keep her in the air