New engine gremlins - frustrating

FWIW, I personally would not be working on the jets at this point; if you are getting this with just light throttle, then the primaries are not really in operation. I would be:
- raising the primary float level temporarily to see what happens; this is not really for a fix but to obtain clues as to which way to go with other things
- looking at vacuum levels to determine operating phase of the carb when this occurs
- adjusting the secondary idle stop screws (assuming this carb has one, which, being made by Holley, seems likely).