I’ve seen things solve problems before, when they shouldn’t have.

But as has been said, the x channel that’s connected to that PV signal cavity in the carb is only there to provide access to vacuum for that cavity when a 4 hole gasket is employed.

Did you try the carb with the 4 hole gasket after you milled the baseplate?
The open gasket looks a lot thicker and more compliant than the 4 hole you’re using.

My guess is if you installed a std 4 hole gasket made out of the same material, and the same thickness as the open gasket you have...... it would run the same.

I’ll add this...... all Holley 4bbl carbs use that cavity for the PV vacuum...... and they all seem to retain PV functionality just fine when used with a 4 hole gasket.

The only reason I thought it had the backwards idle circuit was because of the info provided in the link I posted, which seemed like it was coming from someone well versed in that particular carb.
I’ve never had one of that list number carbs in my hands.

9” of idle vacuum is surprisingly good for that combo.




The fuel that gets added to the main circuit by the PV would only be coming out of the booster(along with the fuel from the main jet) if enough air is flowing through the Venturi to activate the main circuit.