How to modify a 1969 QJ to become a 1970 455 Stage1?

Discussion in 'The Venerable Q-Jet' started by Cutlass, Nov 11, 2018.

  1. Cliff R

    Cliff R Well-Known Member

    I've put this up here before and it relates to installing bushings in the throttle body of your Q-jet (or any other carburetor that has 5/16" throttle shafts):

    There have been a few folks advocating on the Forum’s to use a standard 3/8” drill bit and drill press to bore the baseplate for new bushings, this is a BAD idea as it does NOT keep the drill bit centered in the bore or keep it from going out of round during the drilling operation and making the hole too large/off center. In other words a half-ars method recommended by folks who certainly have little if any experience at this deal, and are better off keeping their day job and staying off the Forums, at least when it comes to giving advice in an area that they really know little to nothing about. Considering how many throttle bodies I’ve had sent here that were ruined using that method, it’s just a good idea to do it once and do it right, rather than risk the possibility of destroying a part that is difficult and in some cases impossible to replace.

    Anyhow, the factory tolerance on the primary shaft was pretty “loose” for my liking right to start with. I’ve measured brand new NOS q-jets at .008-.010” side play on the primary shaft right out of the box. This allows some unfiltered air to enter the engine and within 50,000 miles or so most throttle bodies are worn out past .015”, I’ve seen some twice that number. The installation of bronze bushings, done correctly is a permanent repair for that issue and will set the side play at less than .001”, and should be part of every complete/correct rebuild done on a q-jet carburetor….IMHO….Cliff
     
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  2. Cutlass

    Cutlass Platinum Level Contributor

    ... continued my work
    Adding idle bypass air, which was not 100% by the book because of my early baseplate. But I got great remote support from Ken.
    Trying to find a good spot for the thruholes in the baseplate I used a transparent sheet on which I marked the openings/channels/holes in red for the body and blue for the baseplate. On the top right corner I marked the location in green where I drilled thru the baseplate (and of course thru the gasket).
    IMG_1679_low.jpg
    Next I drilled one 1/4 hole into the left and right cavity of the body.
    IMG_1702_low.jpg
    Then I milled the channels on the underside of the baseplate.
    IMG_1685_low.jpg
    And finally milling two openings into the underside of the airhorn
    IMG_1701_low.jpg
    Converting to electric choke:
    Before
    IMG_1703_low.jpg
    After
    IMG_1722_low.jpg
    Added lever for the TV-cable
    IMG_1721_low.jpg
    Thanks again to Ken for patiently sharing his knowledge and expertise. All of above is not invented by me, I am just a copycat :)
    ... to be continued
     
    techg8 likes this.
  3. Cutlass

    Cutlass Platinum Level Contributor

    ..another couple of hours of work spent.
    My carb was obviously previously rebuilded. I measured the bushings installed for the primary shaft and they are fine.
    As It is my nature to fool around with stuff I countersinked the holes for the primary shaft just so, that there is space for an O-Ring on each side with very little axial sideplay. I will probably never find out if this will really help to prevent air coming thru. But it does not do any harm and makes me feel good :).
    IMG_1849_low.jpg
    For the secondary shaft I customized metric bushings (outer diameter metric, inner diameter imperial).
    IMG_1845_low.jpg IMG_1846_low.jpg IMG_1847_low.jpg
    With regard to Cliffs remark about how to do it the proper way, please note that this is not a standard drill press. So please do not try this at home :)

    Working my way thru Cliff's book I came to the section that all flaps should oben 90° and there should be some kind of a mechanical stopp. Well, my baseplate has this casted nose, but the shaft is short and does not have the pin.
    IMG_1852_low.jpg
    So I took some scrap metal and attached it to the baseplate on the opposite side. Now I have a mechanical stop at 90°
    IMG_1850_low.jpg IMG_1851_low.jpg
     
    techg8 likes this.
  4. Cutlass

    Cutlass Platinum Level Contributor

    I am happy as can be. Today I installed the carb and after just a few cranks the engine fired right up. I did not drive the car, as it still sits in storage, but noticed that idle now is much smoother and that the huge bang and difference in idle speed while putting the car in gear and back in park is now gone. Another couple of weeks and I will get the car out of storage and start the swap to the TH200-4R. When everything is installed I will fine tune ignition and carb.
    Thanks for the support on this board!
     
  5. HotRodRivi

    HotRodRivi Tomahawks sighted overseas

    Sometimes the secondarie throtle blade will actually go past 90, directing air to the front. Sometimes not quite 90 but with the top of the throttle blade in line with the divider. And somwtimes straight 90. one of those have to drive it to find out. What needle and seat are you using. Open window or closed ? How does that electric choke pull off with no choke pull off? How many lines are on your accelerator pump shaft?
    Also hopefully you have a transmission psi gague and that little doo higgy tool for setting the throttle pressure on your 200 r4.
     
  6. HotRodRivi

    HotRodRivi Tomahawks sighted overseas

    Nice work . It must be great having those machines in your garage!
     
  7. Cutlass

    Cutlass Platinum Level Contributor

    Not quite sure I understand.
    I assume with needle and seat you mean the fuel inlet, I have a closed seat.
    Don't know about the pull-off, my carb never had a primary pull-off
    No idea, what you mean with "lines on accelerator pump shaft"
    Yes I got a psi gage with my transmission, but what do you mean with "little doo higgy tool"?
    Thanks, yes I enjoy working with my lathe. And when you have one, you come up with millions of ideas what can be fabricated for the car, for the house, ......
    I learned all that many many years ago during my apprenticeship as car mechanic. Now I am a paper pusher and working on my car or in my little workshop is a nice balance.
     
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  8. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Ralf, your carburetor does have a primary pull off, it is in the very first picture of the carburetor that you posted on page 1.

    I'm sure you know the importance of getting the TV cable of the 2004R adjusted correctly so that the transmission doesn't self destruct. Beyond that, I have no idea what Anson was talking about.:)
     
  9. Cutlass

    Cutlass Platinum Level Contributor

    Larry, you are absolutely right. I meant secondary pull-off.
     
  10. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Right, the secondary pull off was useless anyway, it was there to refine choke opening for emissions.
     
  11. HotRodRivi

    HotRodRivi Tomahawks sighted overseas

    Im sorry , I was thinking of the the ford aod transmission . Psi gauge is all you need for 2004r
     
  12. HotRodRivi

    HotRodRivi Tomahawks sighted overseas

    ActuLly uts a secondary dash pot and its impirtant to delay or slow the opwning of secondaries to draw fuel. The choke pull off would be at the rear and it pulls open the primary butter fly after start up.
     
    Brett Slater likes this.

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