I don't think we totally have the problem solved yet, but we are close. I understand why many would believe there is a need for baffles in the tuned muffler, but it really shouldn't be necessary. The exhaust outlet is smaller than the typical tuned muffler. This is what offers the back pressure. My friends GMS has the new style muffler, and it has the same problem that you are attributing to the tuned muffler. I believe it is stricktly a carburation problem. I should have my friends engine to play with in a couple of weeks. I am not commenting, as I am, without first hand experience. I have one of the older GMS .47's, and it is an awesome engine. It has been run so much, you can't tell that the head was ever gold. Instead of the performance decreasing, it keeps getting better, and I have not removed any of the gaskets in the head. As for the noise, I agree that it appears the engine is noisey, but if you run a hose from the exhaust port to another muffled canister, so you get the engine cumbustion noise away from engine, you will find that most of the noise is coming from the propellor, turning incredible RPM. When my prop is turning 16,200 RPM, the prop noise is incredible. In the air, when the engine can really unwind, there are some undiscribable sounds that come from the plane, that I believe are the prop tips going supersonic. If I could run a bigger prop on this plane, I would, as this is a lot of punishment for the engine. But in that regard, I am in my 5th year with this engine, and it is still going strong. Each .47 should be capable of this performance.

Thanks Wayne, for putting this organized effort together to find the problem. It will pay dividends for all of us!

Andy