new carb car won't run

[surfsup]

I bought a new Holley street avenger 670cfm with electric choke, when I installed the carb the motor started right up and runs great, very responsive when I crack the throttle by hand, I took the car out for a drive and it won’t go, I have to rev the hell out of it to get it moving, the car bucks and hesitates something fierce, and a real bad flat spot, when I advance the timing from 12 to 16 the car runs much better but not perfect, I adjusted the mixer with a vacuum gauge to get the highest reading possible, all hoses are correct, I have a new fuel pump about two weeks old, and I’m running with a stock dizzy, the car ran great with the stock 4180 before I replaced it, any ideas on why I have to advance the timing so much to get this thing to run half way decent? I called Holley but could not get through
you can check my profile for mods to the car.