I am going back to what I said about loading the engine properly, if your Heli's hub and fan are really light your engine may not be loaded correctly, this will allow the engine to rev quickly in which can make your engine starve for fuel. to test this put a 12x5 prop on it and run it.

I had this same problem on my Century 50 Helis with my OS Hyper 50 engine with the OS 8 plug. and now that I have that same engine in a plane with an APC 11x8 and an OS 8 plug it's the best running glow engine I have ever seen !! it will set and idle for minutes and not load up.

Jim