6 pak run bad cold

Thanks for the ideas, the vacuum is rock steady. The carbs are brand new. I did not even open them to check jet size. when I adjust the left mixture screw, it responds, and at 3 turns out, it hits max rpm the right one is almost innefective. It is indoors, at approx 60 degrees. I am using NJ winter gas ( oxygenated I guess with alchohol) premium grade. I thought the vac reading was a little low, but I am reading it at the vac advance fitting, which I spliced into. I am not sure if that is full manifold, or partially ported. I was looking more for needle movement than inches of merc. I have used these 2300 holly's before without issue, but that does not mean I am not lean. After double checking, I do not have the valley pan cross over blocked off, so it does get heat. I have the choke properly hooked up and it functions well. I checked for a vac leak, and so far nothing. It does seem to want more initial timing, but how far is too much. I do not want to fool with the springs and centrifcal adv until I get it idleing right. I took it out, and it runs strong. It is just the eratic idle. If I let it idle for a while, I can get it to settle down at 900 rpm ( calls for 900+-50, and it will stay there until I blip the throttle then it wants to stay at 12-1300 for a while and no, the linkage is not sticking.. I am starting to think either center carb is lean or idle circuit problem, or vac leak that is not readily detectable. The motor was completely done, all mating surfaces machined. It has a cast iron intake. I have built my share of motors, and usually can get them set up less than 2 hours. This is making me scratch my head. Please keep the ideas coming. You all are a big help. I appreciate it!

Thank you

Rich