Results 1 to 3 of 3

Thread: New Memeber, Holley carburetor question.

  1. #1
    Join Date
    Sep 2020
    Southern Ontario

    Default New Memeber, Holley carburetor question.

    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
    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
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	20200912_133222.jpg 
Views:	5 
Size:	99.4 KB 
ID:	10457   Click image for larger version. 

Name:	20200912_133250.jpg 
Views:	4 
Size:	97.8 KB 
ID:	10458   Click image for larger version. 

Name:	20200912_133232.jpg 
Views:	4 
Size:	101.0 KB 
ID:	10459   Click image for larger version. 

Name:	20200912_133313.jpg 
Views:	3 
Size:	100.7 KB 
ID:	10460  

  2. #2
    Join Date
    Jan 2010
    Brisbane, Australia


    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

  3. #3
    Join Date
    Sep 2020
    Southern Ontario


    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

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
About us
Holley has been the undisputed leader in fuel systems for over 100 years. Holley carburetors have powered every NASCAR® Sprint® Cup team and nearly every NHRA® Pro–Stock champion for four decades. Now, Holley EFI is dominating the performance world as well as our products for GM's LS engine. Holley's products also include performance fuel pumps, intake manifolds & engine dress–up products for street performance, race and marine applications. As a single solution, or partnered with products from other Holley companies - Hooker Headers, Flowtech Headers, NOS Nitrous, Weiand, Earl's Performance Plumbing, or Diablosport - Holley products can give you the edge you need over the competition.
Join us