Small Engines (Lawn Mowers, etc.): Craftsmen Lawn Tractor Wont Start, electric clutch, air gap

Question
Never a problem in 7 years w/ Craftsman B&S 21.5 hp v-twin....end of mowing today when I turn ignition their is a strong whirring/humming noise but nothing is spinning and no start. I seem to recall at immediately previous start a stong click noise in engine but who knows.  Where do I start?

Answer
If there is no click voltage is not going across the solenoid into the starter.  If there is a click that there is enough juice to start the motor check your battery it should register 12.6 V DC.  Noise sounds as if it could be the electric clutch or a brake pad hanging up.

If there is no click of the solenoid problem is then circuit so you will have to check the PTO switch, the switch, brake switch, key switch, all connections and grounds.  Also check your fuses to be sure you didn't blow a fuse.  It also remove the blower housing and checked to be sure you still have an air gap flywheel and the ignition coils the gap should be about the thickness of a business card.  The test would be to take 12 V directly to the starter motor and see if the starter will spin.  That would be jumping solenoid from the battery correctly to the starter motor.  If you have a good battery and starter will not budge I would be sure that the engine will turn over by hand remove the spark plugs and turn the engine flywheel to see if the engine easily turns over.  If there is a problem here are telling what it is without disassembling the engine.  When I was saying before that you have to check the safety system I mean that you would check it with a continuity meter to be sure that voltage goes from switch to switch along the wires and through the connectors if 12 V goalless to ground anywhere along the pathway that is where your problem is.  Start by checking out these and if needed contact us again.