[Jackpine]

I think Cody's nailed it.

Several years ago, my neighbor's normally aspirated car developed similar symptoms. I found his fuel filter was clogged. You don't say anything about your fuel filter - have you checked it?

And, I have a chain saw that rather suddenly would not operate at high RPMs. It did fine at idle and at lower speed. I discovered the spark arrestor in the exhaust was clogged, so I just removed it.

My guess is, your exhaust is fine, but I'd sure try eliminating the "easy" causes before looking at the complicated ones.

- Jack