Carbs are tricky.
Quick strange story.
I had a brand new Edelbrock carb installed on my most recent BB build.
I was sure I needed the Cool Carb spacer and was all set to get one becsuse It coughed a lot when I jumped on it and the engine ran too hot.
Tried adjusting etc.
Finally brought it to an elder performance mechanic. He said Im sending your carb to my guy to rebuild it, eventhough its "new", he felt it was too lean and couldnt adjust it out.
Great results.
Since then, the car never ran better, no coughing, runs cool, and much more power than before.
So, "new" really doesn't matter.
(I never installed the cool carb spacer).