ORIGINAL: flyboy9994

Hey Bax

Brand new 55AX broken in per manual, maidened in a new airplane, first 3 or 4 flights fine with no incidents. Engine suddenly starts dying at mid throttle, right where I like to fly. Here's some background:

Can easily duplicate on the ground. Cowl removed to observe fuel line and absolutely no air bubbles or disruption of fuel when engine quits. Engine does not hesitate or sputter, dies like a light switch turned it off. Good idle at around 2800/3000 RPM. Perfect transition to full throttle with no hesitation, Perfect full throttle flight at around 9000/9500 rpm adjusted slightly rich from max rpm. Tried pretty much everything: tuned needles, changed glow plugs numerous times and they looked perfect (OS #8), re-built entire fuel system. Removed and cleaned carb, nothing found. Raised tank to get it in-line with needle valve. Flown with cowl off and engine is definitely not overheating. Same exact problem. Still dies at half throttle...

Here's the kicker: Changed to an OS F plug and problem instantly solved. Put her back together, cowl installed and 10+ perfect flights later with absolutely no mid throttle problems anymore. Do you have any ideas why the F plug would have made such a difference??


Randy