when you put the new carb on, did you allow the car to warm up and open the choke to kick off the fast idle (if it's an electric choke) and then set the idle speed screw? if not, the screw could be backed off too far, shutting the throttle blades completely when it comes off fast idle, and not allowing any air to get thru to allow the engine to idle at all.
a couple of years ago, a friend of mine- who has tinkered with a few cars in his time but is now for the most part afraid of getting dirty- decided to be a manly man and put a new Edelbrock carb on his 71 Camaro in place of the Holley 3310 that he had installed a few months before. he put the carb on, and got it running. but as soon as it got warm, it would just flat out die. he drove it out to my cousin's house for a party a week later- 120 miles away- with it running like tha. and it's a 4 speed car, so it must have been a fun drive.
anyways, i asked him why it died like that, and he told me he put on a new carb that is junk out of the box. i went into my cousin's garage, grabbed a screwdriver, and told him to pop the hood. i cranked the idle speed screw in until it opened the throttle a bit, and told him to start it. lo and behold- it idled right at 800 rpm. we gave him much crap about that for the rest of the night...
you don't plan sincerity.
you have to make it up on the spot.
wanna hear about 20 years ago when i was too smart to know any better?