Secondary Stumble

It may be a power valve issue, and it can be explained that both carbs are lean at that spot of the fuel curve.

FWIW, if you set the power valve opening by idle vacuum it will be wrong.

You need to set your power valve opening by cruise vacuum. For example if you cruise at 16 inches of vacuum, you’ll use the 10.5 power valve, because that is all Holley now offers. Really, at 16 inches it should be 12.5-13.5 but you can get them.

The “Holley” method of using idle vacuum was wrong from the beginning, and it’s still wrong.

12many has an excellently thread where he documents tuning his power valve as outlined above. It is worth looking for that thread and reading it.