Rebuilt carb. Started but died. ??

Put on my carb, freshly rebuilt. I can't get the darn thing to fire up! It did start and it ran for a couple minutes but now NOTHING. Crank and crank, nada. I tried resetting the idle mixture screw to recommended (seat, them 2.5 turns out). No dice. Also tried a few different steps with fast idle screw (engine is cold so choke is closed) and no luck. Any specific recommendations as to how my idle mix/fast idle/idle set screws should be adjusted? What works for you guys? This is a Holley 1920 on a 225 /6 and MSD 6AL ignition. HELP!!