Speedmaster MidRise Air Intake Manifold

Looks like it didn't seal. Got it all together and it tried to start but kept backfiring. Found the rotor had rubbed inside the distributor cap and it was full of metal shavings. Replacing the cap and rotor helped. Now it will start and run at hjgh rpm. But it won't idle. It sounds pretty good. Then starts surging. As the rpms get down close to where it should idle it backfires and dies. Will only run with choke on. So ill be getting another gasket and doing it again.