Small Engines (Lawn Mowers, etc.): Craftman 22 HP B&S engine missfires, craftsman model, ring gasket

Question
I have a craftsman Model 917-272860 with a 22HP Intek B&S engine.  The engine started misfiring when it was running. I changed the spark plugs and there was still a misfire. If I choke the engine slightly I can get it to run smoothly enough to use the mower, but it still runs slightly rough.

Answer
Dan
Here is some trouble shooting tips that may help you.

Problem: Engine misses.
Possible causes:

Spark plug is fouled, improperly gapped, or damaged.
Breaker points are pitted or improperly gapped, breaker arm is sluggish, or condenser is bad.
Carburetor needs adjustment or service.
Fuel line, fuel filter, or fuel tank cap vent is clogged, or fuel shutoff valve partially closed.
Valves not adjusted properly or valve springs weak.

Problem: Engine idles roughly, unevenly, or surges.
Possible causes:

Carburetor is dirty.
Air leak in carburetor or intake manifold (e.g., bad O-ring, gasket, primer).
Carburetor is improperly adjusted or needs service