Craftsman model 917.273461 Yard Tractor
About this time last year I posted a message about this tractor backfiring. I got a number of helpful messages including one about valve lash. It turned out to be a 6 year old dying battery. But the backfiring has started again and I have a "new" one year old battery and I have checked it out so I don't think it's the same problem. I've checked the valve lash and the intake valve on the cylinder opposite the starter seemed to be incorrectly set and I fixed it and that seemed to fix the problem until the engine got some heat in it then it started again. I know it was that cylinder because I used a thermal imagining device on the exhaust tube and it showed a big difference between the cylinder on the starter side and the "off" side (it was much lower). My question is does the lash change so much when the heat increases that it would cause a bacxkfire?
Since this is a 2003 model could the current gas formula be a part of the problem?