Register now to get rid of these ads!

Idle mixture settings on a dual carb set-up

Discussion in 'The Hokey Ass Message Board' started by dmac620, Feb 7, 2011.

  1. dmac620
    Joined: Sep 16, 2007
    Posts: 358

    dmac620
    Member

    I am trying to tune the dual Carter W-1 carb set-up on my Chevy Inline 261. I have looked at the factory settings that list all the information for the stock single carb set-up. The single carb set-up calls for the idle mixture screw to be set at 1 1/2 turns out. Am I correct in assuming that on a dual carb set-up I should have each idle mixture screw set at 3/4 of a turn out, therefore equaling a total of 1 and 1/2 turns out total. I currently have it set at 1 1/2 on each and it seems to be running rich.

    Thanks.
     
  2. F&J
    Joined: Apr 5, 2007
    Posts: 13,222

    F&J
    Member

    No.

    Start at your 1.5 at normal idle rpm, then go in until you see some rpm drop. Then come out a bit. Do that on both carbs, but you really should have a UniSyn to see if both carbs are equal air flow at idle. Or, if you have really good hearing, you can get them sort of close by comparing the air noise from each.

    The reason to get them close is that if one carb is barely flowing at idle, you will not get a good feel on the idle drop when turning the screw inwards on that carb.
     
  3. Flat Roy
    Joined: Nov 23, 2007
    Posts: 533

    Flat Roy
    Member

    Total agreement with F&J. UniSyn is the only way to go. It will turn you rough runner into a dream machine.
     
  4. Pro Shifted
    Joined: May 18, 2010
    Posts: 51

    Pro Shifted
    Member

    I would start with all the screws at 1 and 1/2 turn off the seat. Do not tighten the screw, just barely snug. Then out. As far as adjustments, make sure you adjust all the screws the same amount, in or out. This is as you set the idle with the throttle linkage disconnected and the idle screws so either one will raise the idle.
     

  5. dmac620
    Joined: Sep 16, 2007
    Posts: 358

    dmac620
    Member

    I just got my Uni-Sync in the mail today. I have a couple hours tomorrow to play with the carbs. Spending tonight trying to do some research to have a game-plan for tomorrow. Thanks.
     
  6. dmac620
    Joined: Sep 16, 2007
    Posts: 358

    dmac620
    Member

    With that being said, can someone give me a play-by-play on how to tune with the unisync. The instructions only mention making adjustments to the idle speed screw. There is no mention to the mixture screw. The Carter W-1 only has two adjustment screws. One for the idle speed and the other for the fuel mixture. Do I set the mixture screw at 1 and 1/2 turns out and then only tune with the unisync by adjusting the idle speed screw?
     
  7. dickster27
    Joined: Feb 28, 2004
    Posts: 3,209

    dickster27
    Member
    from Texas

    Did I miss something here. At 12:57 you ask for help and at 1:10 it is suggested you get a Uni-syc tool to equalize the carbie running. Then at 1:14, that's only 4 minutes later you say you got your Uni_syc tool in the mail. I want to know who will ship and get it to you in only 4 minutes.
     
  8. F&J
    Joined: Apr 5, 2007
    Posts: 13,222

    F&J
    Member


    The UniSyn is just a tool to measure or in better terms, Compare the air flow with the other carb or carbs.

    Get your flow exactly the same at idle with carb linkage disconnected. Then make sure each idle stop screw is working against the stop.

    Now with the flow equal, start to turn one idle mixture screw inwards to get a slight drop in rpm, then bring it back out just enough to get that rpm you had. (Most carbs setting info says to leave it at a 25 RPM drop to have it cleaner at idle for emmisions.)

    When you get both carbs idle mixture correct, then you can hook up the linkage and check the high speed flow by re-adjusting the UniSyn valve to allow for more flow. Read the direcections..it's easy to do. If the high speed is way off, you need to adjust your linkage or remove any slop that is causing one carb to flow more.

    One last thing; The Idle mixture screws are idle only, they do not affect mid to high RPM mixture.
     
  9. start out at 1 1/2 turns out tighten in until it starts to miss then back off 1/2 turn and you are set. use the unisyn to synchronize the carbs to the same idle air flow then lock down the linkage..........
     
  10. dmac620
    Joined: Sep 16, 2007
    Posts: 358

    dmac620
    Member

    Gee, thanks Dickster for the play-by-play and time stamps. You didn't miss a thing. I am trying to dial a carb set-up in and had a question about a specific setting on the carbs. The Unisync instructions do not mention the idle mixture screw settings, so I thought I would ask here about it. My apologies...

    Anyway, thanks F&J, that clears up alot of questions I had. I appreciate it.
     
  11. Pro Shifted
    Joined: May 18, 2010
    Posts: 51

    Pro Shifted
    Member


    Set your idle mixture screws to get the smoothest idle or most manifold vacum.
     
  12. F&J
    Joined: Apr 5, 2007
    Posts: 13,222

    F&J
    Member

    On your UniSyn tool; It most likely does not have adapters to fit various carbs. Just use a short length of radiator hose, or plastic plumbing fitting or even a piece of cardboard tube, if it fits good on the carb top.

    The UniSyn will have a flat wide foam rubber gasket to seal to whatever adapter you make.
     
  13. i WOULD LIKE TO say that i think the idel circuit does change the mixture through all speeds

    when setting HC and CO on a 2 gas analyzer and realizing lowest readings on the idle air screws you will improve mileage, we used to do this time in and again and it always made a difference in mileage

    when I was a 19 year old i run 2 Wa1 s on a 235 and they work really nice but you cant buy a manifold for $20 anymore!!:eek:

    I dont want to rain on anyones parade but that is what i was taught somewhere proabbly at Bill Sauers Auto Tech which was over 20 years ago wow where did the time go, did a lot of tune up after that and had a lot of fun learned about the big gap plugs there and running lean mixtures

    oh when i was a kid my 235 got over 20 MPG but who had money for gas then!!!
     
  14. carbking
    Joined: Dec 20, 2008
    Posts: 3,715

    carbking
    Member

  15. Deuces
    Joined: Nov 3, 2009
    Posts: 23,753

    Deuces

    Ever try it with a vacuum gauge and a T fitting??? I never messed with a UniSyn before... What do those things run for brand new??? ($$)???
     
  16. dmac620
    Joined: Sep 16, 2007
    Posts: 358

    dmac620
    Member

    I paid about $30.00 shipped from jegs for it.
     
  17. CutawayAl
    Joined: Aug 3, 2009
    Posts: 2,144

    CutawayAl
    Member
    from MI

    Ditto on the Uni-Syn/Uni-Sync tool.

    As to syncing by ear, a length of vacuum/aquarium/washer hose with one end in your ear and the other at the same point inside each carb works surprisingly well. With care you can nearly equal the precision of a sync tool. If the carb size/design, and the hose being used, allow the hose to be inserted this far, the best spot for the hose is where the butterfly meets the throttle bore. But caution, if you have the hose well into the carb venturi, don't rev the engine with the hose in your ear!

    First, the carbs need to be individually synced with the linkage disconnected or at least not holding one way or the other. Then, the the linkage should be set so both carbs start to open at exactly the same time. Getting this step perfect doesn't matter on a race car, but a street engine will run nicer with the linkage carefully adjusted.
     
  18. Deuces
    Joined: Nov 3, 2009
    Posts: 23,753

    Deuces

    Cool! I think I can scrape that up... Thanks! :D You really should check with a vacuum gauge after you fiddled around with the UniSyn just to see how close they are to each other in idle mixture settings..
     
  19. You also need to have heat under your intake.
    See information at the Stovebolt site.
     
  20. flat34pu
    Joined: Jun 9, 2007
    Posts: 453

    flat34pu
    Member



    fantastic tip, i also am learning to work with the UniSync tool and Vacuum gauge, any way i was trying to figure out why my front carb would not get the bobber to come up to the middle like the rear carb untill i was down looking at the idle screw as i was adjusting it and i saw that i could see day light thru the carb top and the UniSync.
    pressing down on the UniSync and the bobber came up and let me adjust the idle speed, but very aqward trying to adjust the air/fuel mix and holding down the UniSync.
    i am going to take an extra carb today and go to Winchester Auto to find the hose that will fit and make my adapter.

    thanks again F&J great advice.
    rich
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.