Those engines were prone to air leaks, at the carb, back plate and probably through the crankshaft at the nose. I never had a problem with Tower Hobbies .46. it was a screamer and I still have it somewhere in my junk pile. The muffler fits right on OS AX/FS series engines and gives them about 500 RPM boost. Unfortunately they are prone to breaking at the front end and nobody made replacements. I have on a FS .46 right now. MECOA was one of the original US sellers of the GMS, Tower Hobbies forced them out. They may have a few parts lying around for the engines. The engines were all made by Sanye. They made a lot of different makes of engines but would go out of business at the drop of a hat. I think they were last makes of Supre Tiger engines, those are gone too.