RE: Brillelli Engines No Response
Regarding the muffler falling off in flight. That happened because it was not properly secured. Next time make certain that all the threads on the bolts and cylinder are clean. Use Permatex Ultracoper between the port face and the muffler instead of a paper gasket, and use red thread lock compound on the screw threads. Wait for everything to dry (overnight) before going flying.
If you're using a large muffler that provides the mass and moment arm for a lot of leverage on the exhaust mounting flange, consider supporting the end of the muffler farthest away from the flange in some manner to minimize damaging vibration.