This mostly has to do with fuel. This situation has made itself much more evident after opening up the exhaust a little (35% less back pressure or so). So consider fuel setting A: Engine has plenty of torque down low, midrange is good. Pulls hard till a certain (unknown) rpm, and then it just bogs. If you stay on the throttle, it'll bog till it gets back down to under the bad point, where it kicks back in and pulls strong to the "bog point" again, to repeat indefinitely. Fuel setting B, where I've leaned it out a good bit: Little less torque in the low range, about the same in the middle. Pulls the same up high, except the "bog point" is all but gone. It pulls under load to a MUCH higher rpm, and pretty much at redline, it finally reaches the similar conditions of the previously mentioned "bog point" Here's what I think: I think since I opened up the exhaust a bit, the engine is obviously flowing air much better. I think the intake is the limiting factor, and under fuel setup A, the intake simply isn't flowing enough air (really small intake), and it's sucking in way too much fuel, and bogging the engine. I think the richer fuel condition A is really the ideal fuel mixture, but when the intake restricts airflow it just starts sucking in too much fuel. I know I know...typically an engine leans out under higher rpms...but then how come the early "bogging" symptoms disappear when I lean out the mixture. The surefire way to test my theory would be to open up the intake, which I plan on doing. What do you all think about this situation?