This is a reply to my own post because I ran this engine today. The muffler as described earlier worked great. It is 1" x 2" x 5" which adds up to 10 cubic inches for reference, and it is not as restrictive as many Pitts mufflers. The reason for the post is that this engine really ran dirty, I double checked the carb settings and can try another carb, but something just occured to me. A lot of us would like to get the carb closer to the engine to cut down the overall width and this is what I was after. Now is there any comments on the possibility of a shorter carb spacer causing the spark plug to get as black as it did in about 1/2 hour. When I first started it and set the carb, it ran great, but the longer it went, the worse it got as the carbon was building up. Its a new carb and I have other carbs and both brands, but I am still wondering if a typically 1" high carb spacer is required as part of the intake circuit. Anyone else experienced something similiar?
I was using a 50:1 gasoline mix, but it didn't run this dirty when I tried 32:1. There was no smoke coming from the exhaust. The only hint to what was happening was when I pulled the sooty sparkplug, and it was clean when I started. I find it hard to believe it is the short spacer, but I am not positive. I have an ignition analyser and that is next to try.