Carb issue??? Maybe.

[packrat42]

I just replaced my 750 holley with a 670 street avenger holley, as soon as I replaced it, the engine ran fine - like a top. A few days had past I went out to start up the truck, it started up but sounded like it wasn't running on all cylinders. That's because it wasn't - No. 2, 5,& 7 was not firing at all. I pulled the plugs out and cleaned them, checked the gap. Replaced the plugs, swapped around a few wires just to make sure it wasn't the wires. And still the same result. Could it be the carb? I'm sure it could be a number of things but I'm stumped.