I am stumped!

I have a Bolens Riding mower with the 22hp briggs and stratton motor #407777. I had used it a couple times to mow this spring before it started acting up. It doesn't seem to have any power. If i get it to full throttle and engage the blades it starts to stumble and die. I tried disconnecting the kill switch in the seat and didn't help. Here's a list of everything I've done:



Complete carb rebuild

New fuel pump

New fuel lines and filter

New plugs and wires

New coils

Gas tank cleaned out

Fresh gas

Ran with and without air filter

Replaced governor gear

Adjusted the governor arm

Checked and adjusted valve gaps

I even removed the rocker arms and springs so i could put the valve stems in a drill chuck and spin them on the seats to clean them off. (One of the four seemed to have some buildup that smoothed out after spinning it)



I am leaning towards a governor issue since one time i was able to mow with it by disconnecting the governor and wiring it into position. I just had to slow down when i got in the thick grass. But now, after all that, it will start but idles really rough and slow like a Harley motor. Moving the throttle does nothing. Pulling the choke kills it. I took the muffler off to make sure it wasn't clogged and it ran the same. (And really sounded like a Harley then!) If i pull the spark plugs they are both black like it's running really rich. Also there is a little black smoke coming out the exhaust while it's chugging along. So that's where I'm at. Totally stumped. I normally don't have this much trouble fixing something. Which is why I'm here looking for new ideas. I've got way to much money in it to quit. Please help!