What would be the point of PVs in the secondaries? When they open, it's usually because your foot is in the carb. The secondaries will transition just fine without PVs.
As to the front side, YellowRose says IIRC to run a PV a tad under your cruise vacuum regardless of idle vacuum, and I concur with that. If you have your transfer slot properly synced at idle, it will not activate the PV, at idle.
My PV is a 10.5 which is .5 less than my idle vacuum. I have a manualtrans, and can suck the idle down to 550 rpm/4 mph in first gear. I don't recall the engine vacuum down there, but it must be pretty low. The PV stays closed just fine.
How did I choose the 10.5 ?
This has to be done AFTER the primary MJ had been determined, together with the PV. I disconnected the secondaries.
I installed a PV plug and took her for a ride. Got her up to 30mph in second gear,~2500rpm, and rolled into the throttle paying attention to the vacuum gauge and engine response. It is very easy to detect when the engine goes lean. I noted the vacuum, at the stumble, and installed the 10.5. This gave me a nice transition from mains to power. I had been running the idle-vacuum divide by two PV, but I could tell that was not right. I suspected a faulty PV, so ordered up a box of them plus the Morosso checking tool. I calibrated all my PVs and boxed them up in marked compartments. I started with a 5.5 IIRC, and worked my way up to the 10.5, with improvements at every step. The PV plug routine was right on.
When you get it right, the engine will be very snappy with great response. No part-throttle sluggishness.No tip-in hesitations. When you roll into the throttle it will deliver power smoothly like a diesel/electric freight-train.
