Symptoms:
Engine idles fine with glow starter on, advances fine to mid throttle, remove glow starter and it still runs fine. Tune for high speed, and get a nice rpm. I retard the throttle to look for an idle, and just before the stick is full back, it loads up. As soon as I advance the throttle, it cleans up. You'd think...low speed adjustment. I've gone from 1 turn out to 2 1/2 at quarter turn intervals, and it still loads no matter what. I didn't want to go less than one turn in fear of seizing it. It's mounted inverted in a Model Tech P-51, and the tank level (at the output tubes) is level with the carb, putting the klunk about an inch below that.

Sorry if this is an old repeat question, but I couldn't find exactly what I was looking for in a query of the forums.

Components:
Magnum XL 61RFS
20/20 YS Powermaster fuel
Thundercat plug