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Technical Quadrajet help

Discussion in 'The Hokey Ass Message Board' started by Dan, May 15, 2019.

  1. Dan
    Joined: Mar 13, 2001
    Posts: 2,355

    Dan
    Member

    Rebuild a QJ for the sbc is my sons '60 chevy p/u. I installed new bushings on the primary and secondary throttle shafts (after reading that the secondary side probably wasn't needed...) Anyhow, now when the secondary's open they don't close all the way, they stay open maybe a 1/4". I used the proper tooling to drill and bush the throttle plate, but maybe I got them a little bit cock-eyed. Anybody have anythoughts, ideas on what I may have done or how to fix it? Thanks-
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 43,180

    squirrel
    Member

    Find another carb?

    if you can't get it fixed by fiddling with it. It's pretty hard to tell what's going on from here, because I can't look at it and feel what it's doing.
     
  3. tubman
    Joined: May 16, 2007
    Posts: 4,308

    tubman
    ALLIANCE MEMBER

    Whenever I bought bushings for throttle shafts, they always came in multiples (8 or 12 or something). If you have any left, I would just re-bush the shafts again, being careful to get them straight. Also, I bought a longer reamer that makes it almost impossible to bore the shafts cocked. (I put it in the drill and ran it through backwards, running the drill in reverse and pulling it through.) If you don't have spare bushings, I don't know if they sell them in smaller quantities or not or at what price, because I have always bought kits.
     
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  4. Dan
    Joined: Mar 13, 2001
    Posts: 2,355

    Dan
    Member

    I do have more bushings and I do have more carbs...
    I will probably take this one apart piece by piece to see if I can locate where the binding is coming from. This is the first time I have been this in-depth with a QJ so I am committed to try and beat it, just for the education if nothing else...
     
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  5. Rex_A_Lott
    Joined: Feb 5, 2007
    Posts: 940

    Rex_A_Lott
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    Does it bind with the butterflies off?
     
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  6. Dan
    Joined: Mar 13, 2001
    Posts: 2,355

    Dan
    Member

    I assume you are talking about taking the butterflies off the shaft and see if it binds then, I will try that, that is a good idea...
     
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  7. The butterfly alignment is tricky
     
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  8. carbking
    Joined: Dec 20, 2008
    Posts: 2,517

    carbking
    Member

    The proper tooling for installing the bushings, after first measuring to make certain they are needed, is a milling machine with a turret.

    First, measure the clearance from throttle body to shaft. If it does not exceed 0.009, leave it alone.

    If the measurement exceeds 0.009, then make a "pilot" to extend completely through the throttle body, and align the throttle body in your turret vise. Using an end mill, mill into the throttle body but do not mill into the throttle bore. Leave about 0.035 to maintain the curvature of the throttle bore. Install the bushing. Flip the turret, and do the same from the opposite side. Last step is to align ream the bushings. Original spec was 0.004~0.006. The first time I did one I set it at 0.004, and it bound up when hot (guess my tooling not as good as the factory, or maybe the guy using the tooling wasn't as good as the factory ;) ). Re-did the clearance to 0.005, and all was well. That is the spec I continued to use on Q-Jets. Different spec on other makes of carb.

    If you don't have a mill, and you are exceptionally careful, a 50 year old high dollar drill press that has been maintained well might work. Don't try it with the cheap drill presses, or a hand-drill.

    And I know everyone wants to do everything themselves; but in this case if one does not have the proper tooling, "Mr. Quadrajet" (Cliff Ruggles) does the bushings ala carte.

    Jon.
     
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  9. The Shift Wizard
    Joined: Jan 10, 2017
    Posts: 1,355

    The Shift Wizard
    ALLIANCE MEMBER

    A bright light from behind can help spot any butterfly misalignments.
     
  10. Joe H
    Joined: Feb 10, 2008
    Posts: 752

    Joe H
    Member

    If it's binding up on the car, check the base gasket.
     
  11. carbking
    Joined: Dec 20, 2008
    Posts: 2,517

    carbking
    Member

    Also check the throttle body to bowl gasket. Some gaskets aren't cut perfectly, and one needs to be careful in assembly.

    Jon.
     
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  12. Dan
    Joined: Mar 13, 2001
    Posts: 2,355

    Dan
    Member

    It binds off the car-
    took the base plate off and took the secondary throttle blades out and it still bound so that led me to believe it was the shaft/bushings-
    look at the pass. side bushing and looks like it may have a bur or two, the shaft itself also looked to have a little bow to it..
    straightened the shaft and touch and rotated the shaft many times with valve lapping compound, it feels much better now - I will reassemble and let you know if this cured it. Thanks for all the ideas!
     
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  13. Dan
    Joined: Mar 13, 2001
    Posts: 2,355

    Dan
    Member

    Seems to be working good now! I don't know if it's SOP but I think any time from here on out if I put new bushings in for throttle shafts I will lap them with compound.

    Another thing I found which probably as much if not most of what was causing the problem is that the "return" spring that goes on the shaft/linkage on the drivers side - I put another wrap in it before attaching it - I would bet when I assembled it the first time I didn't put enough winds in it...

    Will let you know how it works on the engine, thanks-
     
  14. tubman
    Joined: May 16, 2007
    Posts: 4,308

    tubman
    ALLIANCE MEMBER

    "Carb King" is right of course, but a lot of us are just hobbyists and don't have mills, so we have to come up with alternative methods.
     
  15. F-ONE
    Joined: Mar 27, 2008
    Posts: 1,859

    F-ONE
    Member
    from Alabama

    This is getting into my era.
    Back then as far as high school age kids surmised.....

    The Q-jet was highly thought of with one main caveat.

    They were good for one good rebuild.

    Of course your results may vary.

    Decades later.....I think most are going to need more attention than the standard bebuild.
     
  16. carbking
    Joined: Dec 20, 2008
    Posts: 2,517

    carbking
    Member

    F-ONE - the 1965~1967 need help. But the 1968 and newer generally need only : (A) primary throttle shaft bushing (once), (B) secondary airvalve plastic cam and spring (every 100k miles), (C) fuel inlet heli-coil (once). Once these are done, each rebuild should use a major kit, plus a new choke pull-off, and float (if foam).

    When we were still restoring carbs, we offered a 5-year unlimited mileage warranty for the Q-Jets (even the 1965~1967, but the cost of the restoration was almost double on the early units.) Not too many makes we would offer that warranty.

    The biggest issues for those on this forum are the carbs are somewhat difficult to get to corner at 1G or more (it can be done), and also difficult to keep the bowl full for 600 HP engines.

    Jon.
     
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  17. F-ONE
    Joined: Mar 27, 2008
    Posts: 1,859

    F-ONE
    Member
    from Alabama

    Thanks,
    Jon
     
  18. Good information. I used to have most trouble getting all the outside stuff lined up and working after a rebuild. Now I would take TONS of pictures before I took one apart and have a good manual as well. The last couple I sent out to a local rebuilder, had them back in 2 days.
     
  19. Dan
    Joined: Mar 13, 2001
    Posts: 2,355

    Dan
    Member

    Thanks for all the good info., I hope to get it installed today and see how it goes. I did the throttle shaft bushings, new plugs under the main well, new idle tubes and then the rest of the standard rebuild parts.
    One other question. The body of this carb does not have the usual vacuum port for the primary choke pull off, I am not sure where to plumb it to? Does it use ported or manifold vacuum? I will try to post a pic...
     

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