I have a GMS 47 that was mounted on a cheap GP Rapture knockoff. I took it off and fixed the crash damage on the plane(from a flameout). I was going to mount a different engine on it but the mounting hole pattern wasn't the same.

Anyway, I put the engine on my test stand and couldn't get it to run decently other than wide open(black carburetor). In the process of trying to get the spraybar out of the carb I broke the spraybar. I measured the diameter of the carb and rummaged through my engine parts and came up with a square aluminum carburetor off a late 1980's K&B .61.

After turning the spigot down to .511 and shortening it to .340" I installed it and WHOLE DIFFERENT MOTOR. It will idle slowly and throttle up cleanly to 13,800 with a 10x6 MAS(also OS muffler). I could get more rpm but it already has more power than I need. I need reliability and throttle response.

I will be mounting it back on the plane and will be doing some flight testing soon.

Update, since it was on the stand I remounted the GMS muffler(with 1.21" washer in last third of muffler). Peaked it turned 14,580rpm with the 10x6 MAS and still throttled good(way better than the K&B 61 ever did with that carb!).