Carb Conundrum!

[Duffman]

My 4 screw carbs are in need of some ZTherapy therapy; sizeable vacuum leaks, etc. While I am accumulating funds to make that happen, I picked up a pair of 3 screw carbs locally to have as back up, or to play with, or what have you. I took them apart, cleaned them up (followed the Just DVDs video) and decided to replace my rear carb (biggest vacuum offender!) with the 3 screw alternative. I was stunned how much better the car ran, idle was able to drop down to 700 to 800 rpm (could never get it below 1100), smooth acceleration, etc. Well, being reasonably stupid, I thought I would replace the front 4 screw carb with the 3 screw and make it run better, right? Wrong!! I couldn't get the car to run without having the choke on, front carb doesn't seem to be doing anything when I adjust the air mixture screw all the way in or out and I can't balance the carbs! Very frustrating! I wish I had just left the 4 screw in the front and the 3 screw in the back! When I went back to that configuration, I ran into the same inability to get them balanced and running smoothly without choke. Got to be missing something simple but can't see the forest thru the trees at the moment! Any thoughts?