[philminotti]

Don't know much about the Kinsler system specifically, but I'd guess you're running really rich, which is strange considering you had a dyno tune. Exhaust backfire is usually an exhaust leak, but the flames... Is it both banks or just one? If it was just one I'd believe you're dropping a cylinder, but if it's both I'd head on back to your tuner. You obviously have a big, hairy cam, but it's not a top-fueler for chrissakes.