[mike657894]

I just had my car back fire around 40 and stall out to the side of the road on the last ride. My pertronix coil has a cone shape to its top. The stock style rubber was causing a problem with the cone on the pertronix. The metal wire end was lose fitting which may have added to or allowed the problem to get worse. I spread the contact with a pair of needle nose pliers to archive the tightest fit possible. and did a electrical tape wrap on the cone then on to the wire to retain it and water proof it. May not be your problem but check that area. It would run fine then up over 40 back fires. If you find a rubber that fits the top better post it on the barn.