New motor won't start........Help?

[n737nc]

Hey guys,

Just installed my new motor this weekend. Tried to fire it up, and nothing

It just turns over and does not even try to fire. If you give it any gas at all, it backfires through the carb.
It sounds like a timming issue, but where to start? The distributor is stabbed correctly, all of the plug wires are in the correct order.

Any ideas? Could I have the cam 180 degrees out? Should I take the distributor out, turn the crank 360 degrees and restab the distributor?

Any help is greatly appreciated.

Thanks,
Nick