No matter what the following two conditions must be present in order for the Whizzer to fire, the green terminal on the coil must be ground, and secondly the green connector on the CDI must NOT be ground. The "stop/run" switch on the right control "shorts" the CDI green wire to ground in the "stop" position. The key switch "shorts" the CDI green wire to ground in the off position. The green wire to the coil should always be ground, and if not, "fix" it. The best way to check a spark plug is to replace it [never hursts to have an extra plug]. You might also check the screws that hold the alternator plate to the motor [must remove the flywheel], as I have seen a few work loose. Use blue Loc-tite on the screws.
Hope this helps,
