Thanks for the input, all. I have a few updates. I found there was a small leak at the solder joint where I soldered the tubing on the carb vent plate. I patched it up so the vent tube is airtight. I switched to an NX 23x8 prop as I think the 22x8 was not enough load. I went through a complete retune of the engine with a fresh mix of 87 octane and Amsoil 100:1 mixed at 90:1. I have the engine running fairly well turning the prop at 6800RPM’s with a few exceptions. With the low end lean enough for a clean transition with little popping/burbling on the low end the engine will barely idle at all on the ground. I have to keep goosing the throttle or the idle will slowly drop and die. This is huge annoyance when I’m waiting for my turn onto the flightline.. It seems fine in the air, though. If I richen the low end just a little for a solid idle and snappy transition, it’s still very rich in the air – like popping and missing rich. I believe my assumption that the engine was loading up and dieing in an inverted, low-throttle situation was false. I’m now fairly certain it’s leaning out and dieing. In an inverted elevator or flatspin the throttle becomes unresponsive and the RPM’s quickly drop (like it does on the ground idling..). If I’m lucky I can catch it in time, drop the nose and avoid a deadstick. Throttle response also seems a little funky in rolling harriers, but it’s manageable.

Long story short, too rich upright and too lean inverted. I can’t find a happy medium. The engine runs like a champ as long as I’m not inverted with a low throttle setting – which very much limits my 3D repertoire.. I’m at the point where I almost don’t enjoying flying my 50cc plane because I fear a deadstick…