Results 1 to 4 of 4

Thread: HP Ultra primary idle adjustment.

  1. #1
    Join Date
    Sep 2016
    Posts
    5

    Default HP Ultra primary idle adjustment.

    If I was to upgrade an older 850 4781-2, which is not four corner idle adjustment, only primary. Do I need a secondary metering block with idle mixture screws and replace or modify the base plate? I see nothing mentioned in the instructions.

  2. #2
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
    Posts
    1,944

    Default

    You need to get a secondary metering block with mixture adjustment. Drill the secondary discharge port in the throttle body to the same size as the primaries, (under the butterflies). And also plug the channel in the top of the base plate so all four screws will be independent of each other. This thread might help you: https://www.hotrodders.com/threads/4...y-4150.344154/. Gary
    Regards, Gary

  3. #3
    Join Date
    Sep 2016
    Posts
    5

    Default

    Rereading my post, I didn't ask what I wanted to know. The 134-302SA, 850 upgrade body kit. With this function properly with the parts from a 4781-2, which has primary idle mixture screws only. My 461 BBC doesn't have a hugh cam, don't need four corner adjustment.

  4. #4
    Join Date
    Jan 2010
    Location
    Brisbane, Australia
    Posts
    1,944

    Default

    Your 4781 already has a non-adjustable metering block on the secondary.
    So you can swap the main body, straightforward.
    I'd put a kit through the whole carb while you're it.
    The only benefit you will gain is potential more HP from better airflow, and air bleed tuning ability. Gary
    Regards, Gary

Tags for this Thread

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