Ok, so yet again, I've got a busted engine.
It's a 2006 Briggs&Stratton 8.5hp OHV mounted on a Craftsman snow blower.
It starts first pull, and runs ok for a bit. Then after about a minute, it starts surging, and then after another minute, it stalls.
What I did is rebuild the carb, to no effect.
Now the interesting thing is, if I hold the governor at a fixed throttle with my hand, it will run super smooth, and forever.
The troublesome thing it, the carburetor has no adjustment screws, and it has a fixed throttle.
Thanks for any help!