I had to park my Cuda for a couple of years. I would occasionally start it and let it run for a while. I had to move my car to another space. When I tried to start it, it was backfiring thru the carburetor and exhaust. It would barely stay running. I checked points, plugs and wires, all good. Rotating the distributor to advance or retard didn't help. I would check the timing but it wouldn't run long enough to test it. When I rebuilt the motor many years ago, I removed the original chain that had nylon teeth and installed a metal chain and new gears. I'm suspecting the timing chain jumped a tooth. Any thoughts?