flathead idle issues...help!

[rodderbilly]

Hi all....i need a little help and input....i have in my flathead 2 holley 94s....one has a choke the other not...carb with choke is on rear....problem is this...engine sometimes backfire ,the front carb sucks a lot of air.....when i put a hand on front carb leaving only a little space for air the car idles.......i change the power valves from 7.5 to 4.5....but engine not idle yet...what could be the problem?thanks