Holley Carb help

I put a new 600 Vac. sec. Holley on my car this weekend ran fine at first.

My problem came when it backfired a few times while rev. it up and then the car would'nt idle below 1500rpm, I turned to idle screw all the way out still no change

my question is if I blew out the power valve would it cause the car to idle at a high RPM any thoughts