Is it a new carb? You could just have a vacuum leak. The lower your rpms the more your vacuum is effecting your engine. Have you tried using propane, or spray some carb cleaner around the gasket on the bottom of the carb. I would spray a little everywere their is a vacuum line or port. Also make sure your chock is opening all the way.
It is a rebuilt carb. Yep, the choke is open fully. I only have the pcv line with a T in it for an in cabin vac. line (1/8th"), but took carb cleaner around the thing and didn't have any stumble etc, so I do not suspect vac. leak, at this point.
First determine for sure that you dont have a vacc leak......
Otherwise Its loading up........are you sure the floats are adjusted properly?
Floats are not heavy?
Today,Holley has poor quality control..............
I drove it around today and drives great except for this idle issue. I went ahead and just checked the float levels and secondary was spot on and the primary was too high, so I adjusted it, and got the level down to spec. It really didn't help though. I mean, it was running good for a min or so and then it started back to before. It seems maybe a touch better, but not too noticable.
One other thing, is that I am 2-1/4 turns out at idle-seems like a lot to me. I have tried more and less and this seems to give me the highest idle vac. Has the stock 66 primaries, and 39 secondary plate. Secondaries are 1/4 turn off seat and everything appears to be in spec.
I can give it a throttle shot, and it goes back to good idle, 14" vac. then bounces a little down to around 13.5, then 13 etc and hovers there basically but seems to be missing... but it "resets" everytime I give it a tap on the throttle.
Oh, and now that I lowered the primary float, I seem to have a slight sputter off idle. Don't know if this means anything, but didn't change the accel stuff at all. At least it sputters when the engine starts running rough, but I can blip it right after blipping it to "reset" it and it does not sputter.