ORIGINAL: Aussie_Knife_Edge
I must say that this model and engine has performed faultlessly until a few weeks ago when outside loops were performed.
If it has only just appeared,have you changed anything?
Maybe it is a simple as a pinhole in the fuel pickup tube in the tank.
I had a model once where a similar thing happened, I opened the tank, changed the internals and messed around with all sorts of stuff. I eventually found a pinhole in the aluminium tube for the pickup piep just near where it exited the stopper inside the tank.