Me again... I have never had so many problems with a YS engine. Must be losing my touch.

Anyway, Hyde soft mounted YS140L, running Wildcat Helimix 30% nitro, Hatori piped, inverted, OS F plug. Installed in 2M wide body with tank on CG. About 16" of fuel line from tank to engine. Only thing in fuel line is one TEE fitting and a fuel filter. Tank holds pressure for days. Lines in good condition and clunk is free. Fuel reg and filter are clean. Valves are set properly. Engine has very good compression. No air leaks that I can find. All seals / rings new this year.

Engine will shut off on extended down lines of about 5 seconds or more.

Seems like it only happens after at least half the fuel is gone. Cannot reproduce problem on the ground. Engine will idle at 2000-2200 RPM for minutes and will still transition to full.

What I notice: down line at idle. Prop always turns. As I apply throttle in level flight, I can hear the intake note change, but engine is not lit, but prop is still turning. I'll blow a little smoke (probably just clearing existing exhaust from pipe) and then the prop stops completely.

I'm stumped. It won't always do it. When it does die I have no warning. I've considered on board glow drive, hopper tank, higher idle, changing low end mixture, but don't really know why the engine is shutting down so I don't know where to start. My gut reaction is that the long lines are allowing a large enough air bubble to be passed on down lines that the engine dies: bladder tank or header tank would fix. However, others have indicated that they do not have this problem in similar setups. Any ideas on what I'm doing wrong? Thanks in advance.