It could be three things.
1) The contact points on the flywheel and coil have gotten rusty and need to be cleaned to get spark again.
2) Something is grounding out the coil. There is a small black wire that attaches to the coil which grounds it out to stop the engine. Possibilities are: a bad ignition switch or a safety switch issue somewhere. If you unplug the black wire from the coil you can see if this is the issue. Be aware you will not be able to stop the engine by turning off the switch. You will have to plug the wire back on to stop the engine if it starts.
3) A bad coil.
493880S
.030
The 14.5 hp ohv Briggs & Stratten engines require a 0.30 in gap
.30"
0.030"
0.030
.045
0.030 is the gap for briggs and stratton 4.5 hp mower
Spark Plug Gap is .030
15 HP.
.030
22 thousands