I have an OS 91SII 4 stroke engine. The engine or tank has not been changed since the last flight. It has always started very easy and zero problems with it. Same fuel, changed glow plug, but no difference, checked gap on valves and they are fine.

Problem: Remove the fuel line and fuel flows through the line as it should. If you choke it and get fuel into the carb, then it fires and quickly runs the prime through and stops. Without choking, it is more difficult to fire. While it is running on the prime, if I advance the throttle, just slows down and quits. It just seems like a fuel flow problem, but can not find the problem.

Any ideas or help?