I suggest you go through a step-by-step process to find out what is wrong. First, test for a spark directly from the plug lead to ground (no spark plug). Be sure the speed control is set in the start position (maximum speed setting). If there is no spark, you have an ignition system problem. When that happens with a Briggs engine, the first thing to suspect is a problem with the kill wire circuit. Remember that when the speed control is set all the way to minimum, the kill wire is grounded at the governor base. Check the movement of the speed control lever at the governor end, and make sure it is moving away from the stop position. If it is, the next step will be to remove the cooling air cowl and make some checks at the Magnetron ignition unit itself. The first check there would be to look at the gap between the flywheel and the coil's steel yoke. With the flywheel rotatated so that the magnet is against the yoke, a standard visiting card should just fit between them. The coil should be tightly mounted, not loose.
If you get this far with no spark and no reason found, the next step is to isolate the kill wire, either by disconnecting it from the Magnetron, or by disconnecting the other end of it from the governor base and unthreading it so it is kept right away from the mower for its whole length. Try for spark again. If still no spark, you will need to remove the Magnetron (2 mounting screws) and inspect it and its mounting area for rust and bad contact.
At that point, please come back to us with a report, some pictures, and details of your engine (the very long series of numbers stamped on the cooling air cowl).
