New Memeber, Holley carburetor question.

[Elite Carpentry]

Hello everyone. New memeber here from Southern Ontario. I'm trying to get my car back on the road and looking for some carburetor assistance. Here's what I have:
750 Holley Double-pumper
4BBL
Carb # 4779-6
Carb model # 4150
The question I have is, when I took appart the carb to clean, as it's been sitting for years and replaced old worn out parts with new ones, I noticed that one of the power valves is a blank insert as the other one is a 6.5. Why would only one side have a power valve and not the other, as the kit comes with two of the same for both primary & secondary sides? I have exploded views of this model and they show both as power valves. I have books about Holley Carbs, but just not getting the info needed and I've reasearched it as well and same. The info that I can only get is when used for racing the manifold vaccum fluctuates at idle and low speeds so you must install a power valve that won't open & close. (A blank?)
Any other info you guys need, I'll try and get it. Thanks in advance. Jesse

[Gaz64]

A power valve blanking plug would be used on the secondary side, and the secondary main jet would then be jetted up for a 6-8 jet size difference primary to secondary. This is generally done if your car experiences hard G forces on launch, drag racing, etc.
60 foot times faster than 1.5 can certainly benefit.
The PVCRs (Power Valve Channel Restrictions) can be uncovered from the fuel sloshing to the back of the bowl.
So examples could be a stock carb with 75 mains F,R, and 6.5 PVs F,R, versus 75,82 mains F,R, and 6.5 primary PV, and a secondary PV plug.
Your 4779-6 could have come with a plug from factory. You get a spare PV for if you have a failure in the future. Gary

[Elite Carpentry]

Makes sense. I'll have to take a look at the mains and see what I have before I go any further. Thanks alot for the reply. Jesse