help please

So I just finished installing a new cam and heads in my 383. I am having a he'll of a time getting the initial timing setup. It turn over and sounds like it wants to start, but nothing. I tried retarding and advance all that seems to do is backfire through the carb. I'm at a loss.

Either 'timing' Distributor is 180* 'out', or you're Firing Order {Spark Plug Wiring} is incorrect.

If it is firing back through the Carburetor, you are at least getting proper 'spark'.