Backfiring out carb and wont run right

buddy called me after getting a new Edelbrock on his 390 Galaxy. Ran like crap, no idle, etc. turns out the power brake port was wide open in the back and the plug was rolling around the bottom of the box. Sounds like a vacuum leak to me, and check your plug wires, could be 180 out. I had a 351C that actually started 180 out!