66 273 4BBL Carb Help

I love this site, great people and I've learned a lot eading threads over the years. Hoping for a simple solution but after reading a few other carb threads probably not. I have the original 4122S carb on 273 Hipo C.A.P that has been rebuilt and bench tested. Engine has been rebuilt, and only thing that changed was bored 30 over. Engine just won't idle properly and eventually boggs down after a minute or two. Sent it back to the guy who rebuilt the carb and he opened the needles a hair to let more flow through and that didn't helped at all. In the process of trying to break in the cam my mechanic installed an Edlebrock 600cfm and it runs and sounds great. That was the reason for opening up the needles on the 4122S which is 500cfm. After spending $375 to have the carb rebuilt I'd really like to use it. I do have a 4305S carb that we can try but I'm looking for suggestions to try and make the original work first.

Thanks for any advice.