First check to see if you have a safety switch problem. Do this by disconnecting the coil ground wires. There is a black wire coming from each coil. remove them and see it you have spark. The engine should run but it will not shut off without these wires connected. If you still do not get and spark from the coil(s) they ether are not adjusted closely to the flywheel or are bad. I have had both coils go bad on a 420 engine a few times. cant explain why. To test safety switches just use jumper wires between the connectors until you find the one that is bad. Seat, Brake, PTO (blades), etc.
HI J.R. I CHECK THE GROUND WIRES ON THE COIL ,BUT WHEN I DIDTHE COIL BY THE STARTER THE ENGINE WOULD NOT TURN OVER .WITH THE COIL NEAR THE FLYWEEL,I STILL HAD NO SPARK.DO YOU HAVE A DIOGRAM FOR THE SAFTY SWITCHES? THANK YOU PAUL IS THERE ANY POINTS UNDER THE FLYWEEL?