Hi Guys.
Here is the problem. Ihave a 12.5 Briggs engine fitted to a ride on. The plug sparks, the plug is wet with fuel. Starter motor turns the engine over well but the engine does not fire. I have fitted a new regulator which has made no difference. Oil level is fine. Safety swithes on ride on are OK. Can any body help?

The most common problem that you might have is a sheared keyway between the flywheel and the crankshaft. If you pull the nut off the top of the crank you can see the groove in the crank and a groove in the flywheel. There is an aluminum keyway (square stock) that keeps those two items lined up. They must be perfectly in line. If they are even a little off it will fire at the wrong time and the engine will not run.