I have a 1996 GT242 that quits after an hour or so. I checked the gas cap and I thought it was getting fuel. The first couple times it did this it didn't have spark when it quit... So I replaced the igniter today. It ran for almost two hous and i thought all was good... then it just backfired and quit. I let it cool for several hours and it won't even pop. I took out the plug and it's getting spark. Where should I go next?