There are a couple of different reasons and engine may run poorly, valves out of adjustment, dirt in the carburetor or a sheared flywheel key. It sounds like you’ve covered most of the bases. Did the engine backfire when it stalled? If it did, the flywheel key was probably sheared. If it didn’t it may be the valves.
To adjust the valves you will need a blade type feeler gauge that has 0.04 to 0.06 blades on it. You will also need a wooden dowel or pencil.
To adjust the valves follow the step below:
Remove the spark plug.
Remove the valve cover. Being careful not to damage the gasket as you can reuse it.
Turn the flywheel slowly clockwise to bring the piston to Top Dead Center (TDC). Use a small wooden dowel or a pencil inserted into the spark plug hole to feel the piston come to the top (If you use a pencil put the eraser end into the hole).
When the piston is all the way to TDC, mark the dowel with line at a reference point somewhere on the engine.
Remove the dowel and make a 2nd mark 1/4 of an inch further up the dowel.
Reinsert the dowel and keep a slight pressure on it while turning the flywheel clockwise until the 2nd mark is at the same reference point.
Adjust the intake valve to .004 to .006 of an inch, Measured with a blade type feeler gauge. There will be a nut and set screws inside the nut loosen both of them.
Tighten the nut until the proper gap is achieved.
While holding the nut, tighten the set screw securely.
Repeat steps 6 & 7.
I've included a link to a video on
How to adjust the valves on a Briggs & Stratton engine
I've also included a link to a video on
How to clean a Briggs and Stratton carburetor
If I can be of further assistance please feel free to follow the thread with any questions you have along with the specifics.
I hope this helps.