Please help I replaced the top end in the 426. Im trying to learn to do work myself.! Now that I put it together it is not running properly. It started up with the choke on but backfires and cracks with throttle and dies if you try to let it idle. my rubber boot between the carb and cylinder seamed old so I replaced it, but no change. Cleaned the carb while I had it off, no change. I tried to re time it today and still no luck. When I replaced the piston, rings ect ... I turned the engine over to make sure I had the piston and rings seated properly. The cams were not in when I did this/ is this my problem? Wrong tdc or something backwards? While replacing top end I removed the valves and replaced the valve guide seals and cleaned the valves (that were extremely dirty, especially with build up at the bottom of the neck).