Small Engines (Lawn Mowers, etc.): Carb/Start

Question
I have a briggs and stratton Model 28N707, 15.5HP, Type 0171 engine on a craftsman riding mower. It was given to me after sitting idle for about 3.5 years.  IT will not crank on its own.  If I pour a little gas in the air intake area and then try, it cranks for only a few seconds, but will not stay running.

I soaked the carb in Mechanic in a Bottle overnight and ran it through my fuel lines.  Same results.  Any ideas?

Answer
When you say crank do you mean the engine will not turn or it will not start. If it will not start it is a result form sitting which means the gas has varnished and it needs to be drained out completely. I would install a new fuel filter, and put on a new gas lines since they begin to dry rot from sitting. After this is done I would take the carb off and clean it with carburetor cleaner, you may want to rebuild it, but if it were mine I would buy a new carb. If the engine will not crank it could be because the valves are out of adjustment. On these engines the intake is set at .003-.005 and the exhaust is .005-.007. Let me know if you need more help.