Small Engines (Lawn Mowers, etc.): craftsman 12 HP lawnmower, briggs and straton, craftsman riding lawn mower

Question
I have a 5 speed 38" craftsman riding lawn mower.  It has a 12 HP briggs and straton motor.  When I try and start the mower, gas spews out of the carb like a fountain.  Also, if the mower is stopped, gas fills into the carb and then starts to leak.  I wonder if I need to make an adjustment on the carb?  I tried to make a few adjustments already, but that did not help.  I would like your help and expertise in trying to diagnose and fix this problem.
Thanks,
Mike

Answer
There is a problem with either the needle and seat or the float. You need to remove the carb and inspect the inlet needle and seat for wear and replace accordingly. If the float is the problem, it won't float because it has a hole in it (you should hear fuel in it if you shake it). It's also possible there is just a piece of debris between the inlet needle and the seat.  Hope this helps.