The only thing a PV will do for that application is help keep the plugs cleaner when you’re putting around the pits.

I like the rating to be pretty high so it opens early on in the throttle opening at the starting line.

I’d also prefer it not to be real close to the vacuum reading at idle, if possible, so it doesn’t fluctuate open/closed during idle.

I’d be using something around 6.5-8.5........ and if it’s just open all the time at idle, that’s fine(usually helps with throttle response in that type of application).

Without seeing the carb myself and what’s been done to the low speed circuits, my suspicion is that the conversion from a “reverse” idle circuit to a “normal” idle circuit isn’t quite right for the application.
I’d want the primary idle/transition circuit(including ifr/air bleed sizing and placement) to be laid out just like a normal non-emmisions calbrated carb is.

In having messed with this stuff for almost 40 years........ my experience is that nothing is better for isolating a potential carb problem...... to the carb............than swapping it for a known good carb.

Basically, my viewpoint is........ if you put something like a QFT Q-750 on it......., assuming that carb was working as it was intended to........ the wet plenum and fouled plugs would go away.
And if that happened, you’d know the problem was strictly a carb issue.