Small Engines (Lawn Mowers, etc.): Simplicity Landlord 3410, woodruff key, head gasket

Question
Hey Eric,
   My brother has a Simplicity Landlord Lawn Tractor 3410 with a 10hp Briggs engine. It started missing badly and pouring black smoke out of nowhere. It was running fine and just started this. He has replaced the spark plug, points, condenser, coil, head gasket, Carb, changed the woodruff key, changed the gas, checked the valves, and performed a compression check that read 115 psi. He also disconnected the starter and battery with it running to rule out any shorts. It will run at low idle but it is terrible at mid and high range throttle.
   Any suggestions???

Answer
Sounds like the engine is running rich, extremely rich.  Did you replace or rebuild the carburetor.

Does the engine smooth out if you remove the air filter?  Can you starve the engine, to the point where it dies, if you turn the carburetor needles in?

Eric