checked the float bowl and the drain screw is on the right side as you sit on the bike. I pulled the muffler and started it up and it did the same thing, so I can assume it isn't the muffler? The tube inside the muffler is clogged with a soft soot. ';m doing my best to clean it out but basically I'm just pushing a screw driver in and out of the tube. Since it does the same thing with the muffler removed should I look at the carb? It just seems like it's hitting a rev limiter at very low rpm??