Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Is there a fuel filter between tank and carburetor> Do you have good flow to the carburetor?
Yes, fuel filter? Was it changed? Does engine have any power?
The hunting is sign of lack of fuel, so changing the fuel filter should be first thing to try.
Is this gravity flow or is there a fuel pump between tank and carburetor. This is OHV engine, have the valves ever been adjusted? .004 to .006 inch intake and exhaust.
With this being gravity flow, for test, remove the fuel filter and test.
?? And valves have the correct clearance. It is possible that you have a valve that is not seating! Would show on a leak down test, but not compression test.
It takes and air compressor and adapter with gage, where you put air into cylinder, and then shut it off, to see how long it holds pressure and where any leakage shows up, as through the valves or the cylinder!
I doubt it will help, but try to add a small amount of tension to the springs on the carburetor linkage. Do not add much, as added tension will change maximum rpm.
Most auto supplies would have a leak down tester to rent.
The governor lever can be moved on the shaft, that goes inside the crankcase. but it is very sensitive to any change. It you want to try moving the lever on the shaft, mark the two parts with a scribe before loosing so it can be put back to it's original position. The lever is loosened and the shaft has a split end , that lets you turn the shaft in tiny increments, one way or the other to change governor setting.
Its not a certain, try one way and see it fit gets worse or better.