Holley/Demon Carb stumble

Love to see you do this:
Set the regulator to 6.5psi, set the ball valve for 5.5 and 6.0psi(test both), and see if it’s still in the 50 second range per gallon.

That would represent the carb inlets just somewhat open but the regulator set lower. Should be easier on the carb's inlet system to control and have less turbulence and aeration.
Then you could try with the ball valve set at 4 psi, which would be the same pressure drop between the regulator and the carb as in last night's test (9 psi to 6.5 psi).