318 wont start and backfires out the carb?

This is strange, Im trying to hear the roar of open headders (just installed) and my 1971 dart will only pop out the carb?

I have tripple checked my plug wires and they seem ok. I had the rotor off and the cap sitting on the manifold when I raised the engine for installing the headers so I dont think I dammaged cap or rotor.

What the heck could have gone wrong?
What else may I be overlooking?

Thanks so much for all the help.