Motor hard to start, runs for a couple seconds then dies, backfires through intake

[61Chevy454]

So I'm rewiring my truck, and I'm trying to make it run. It ran before I pulled all the wiring and it will somewhat run now, except after a few seconds of really rough running, it dies. It also backfires through the carburetor. I had to wire in a Mallory HyFire VI box because I have a unilite distributor, and everything worked before I took the wire out. I checked the wiring diagram and everything is where it should be. What should I be looking for? I desperately need to make my car run. It's a 454.

Thanks guys!