Craftsman Riding Mower 21 HP turns over fine but will not start?

Dirt is the Number 1 problem with both 2- and 4-cycle lawn mower engines. This is because the engine works almost at ground level where spinning blades generate a whirlwind of dust that chokes engine air filters, fuel filters and lines, spark plugs, controls and other parts.

PROBLEM: ENGINE WON'T START:
The procedures:

• Are the engine controls properly set on "start"?
• Does the engine have fresh fuel in the fuel tank?
• Is the tank more than half full of fuel? Is the spark plug wire attached tightly to the plug?
• Going down this checklist:

1. Trace the sheathed control cable from the handle of the equipment to the throttle on the engine. The throttle should be fully opened with the control handle setting on "start". As you move the control lever from "start" to "fast" to "stop", the cable should be clamped so that it operates the throttle. The cable can be slipping in the clamp just enough to cause the throttle to malfunction.
   Move the throttle control to its open, or "start" position with you fingers. Or, push the throttle forward, toward the front of the engine. You may have to move the control lever with your other hand to ease the throttle open. If the throttle cable is slipping in the clamp, tighten the clamp screw with a screwdriver after you push the cable forward toward the engine until the throttle stops. The throttle is now in a fully open position. Set the handle control lever on "fast" or "start" and tighten the clamp.
2. If the engine now starts, let it run several minutes. Then pull the control lever to "stop". If the engine slows but does not stop, loosen the cable clamp and pull the cable just a tad toward the control lever until the engine stops. Then tighten the clamp. Go through this sequence until the mower stops and starts on command of the control lever. No gas or dirty gas, mower manufacturers and professional lawn mower repair persons report, are two big troublemakers for engines that won't start.
   Dump out the gas in the tank in a safe spot and refill the tank—even though you think the fuel is perfectly good. If you are just starting the mowing season, start with new gasoline; last year's gas can be weak.
3. Fill the tank with fresh fuel. Low fuel in a tank sometimes can prevent starts. This sounds strange, but it is true.
4. Spark plug wires, through engine vibration, can become loose. The engine doesn't get any spark so the fuel can't be ignited.
   Pull the wire off the plug. You'll notice a thin metal "socket" which goes over the plug terminal. With pliers, carefully crimp the metal socket. Now replace the socket on the plug terminal.

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You can try this testing procedure too:-----

The first thing I would do is disconnect the ground wire on the ignition module; it will be a small, usually black wire. With the spark plug removed and the coil ground wire dis-connected, turn the engine over and check for spark. If you have spark then you know the coil is fine and the problem is a safety switch.

Probably the easiest method to trouble-shoot your problem is to use the continuity function of your meter. Connect one of the meters leads to the coil ground wire, with the coil wire still dis-connected, and the other end of the meter to ground.

Start tracing the wires back from the ignition ground wire to the key switch and each safety switch. Make sure you the mower levers and stuff are in the start position. If you're lucky you could also start dis-connecting each safety switch. When the meter stops beeping you know that the ignition ground is no longer grounded and the switch you just dis-connected is the likely problem.