pelham,
I've always had some random problems with my 4*60 engine quitting when in flight. I've had the same problem with two different engines so I know it's not the engine. I have replaced the fuel lines and tank and still the same problem.
I read an article on Uniflow fuel system setup and I think it is worth a try. Here is the link to the article:
http://www.fraserker.com/heli/uniflo...flow_works.htm