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Rebuilding the Quadrajet

Discussion in 'The Garage' started by 84gmcjimmy, Apr 3, 2005.

  1. 84gmcjimmy

    84gmcjimmy 1 ton status

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    Alright I got the old carb off the engine in the Jimmy without too much trouble. Although I spent 30 minutes looking for a 1/2" wrench and couldn't find it, ended up just using a socket instead.
    I'm pretty sure there is 6 things I took off (labeled them) which went pretty smoothly.
    Here are some picstures:


    Carb off the manifold:

    [​IMG]

    side by side...old one is on left, "new" is on right:

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    Why is this open on the old one:

    [​IMG]

    But closed on the "new" one:

    [​IMG]

    Whats this, and why does the new one have it, and the old one doesn't?

    [​IMG]


    Old:
    [​IMG]


    Why are these different on the side of the carb? Will the "new" one work on the Jimmy still?
    "New":

    [​IMG]

    Old:

    [​IMG]

    Please excuse the messy bench...thats why I'm not taking it apart yet, I have to clean it up.

    Do I need a stand for the carb? Or can I just set it on a block of wood like I do now to get the stuff off the bench?
    If I told you guys the numbers on the carb, would you beable to tell me what it means?

    Thanks...more pics later as I continue..tomrrow I will phone about a rebuild kit, and pick up some carb cleaner.
     
  2. MEPR

    MEPR 1/2 ton status

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    The only thing i noticed that might be a problem is that the "new" one dosnt look like it has the nipple for the evaporative charcole canister. So the "new" one might be fore a pre emmisions truck. Hopefully someone else who knows more might chime in. Also your "new" one has a watter choke on it instead of an electric.
     
  3. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Stave, what are the numbers on both carbs?? I'm betting the "New" one isn't designed for your application... They made many different configurations for different vehicles and applications, even ones specifically for Marine engines... so tell us the numbers and we'll tell you what they mean.
     
  4. 84gmcjimmy

    84gmcjimmy 1 ton status

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    Here are the numbers: (I think these are the right ones, they were verticle, close to where it says "Rochester Quadrajet" on the side...

    OLD:

    17085238
    3424 HTB


    NEW:

    17058204
    3567 BHT


    I hope I can use this one! :crazy:
     
  5. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Lets see... the 170 on both means they were built after 1976... the 58 on the new carb means it was built in 1978, and the 85 on the old means it was built in 1985. The 2 on both means 49 state legal (not CA legal), the 3 on the old carb means it was built for a Cadilac, and the 0 on the new means it was built for Chevy/GMC. The last numbers all that matters is that it's even for an Auto Tranny, or odd for a manual, both are even. I have yet to figure out the difference between BHT and HTB, nor do I know what the lot numbers are for yet.
     
  6. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    the overflow vent is missing on the new one, but you should be able to remove it from the old one and reinstall it.

    your old one is electric coke, and the new one is a hot air choke.

    your new one came from a mid to late 70s truck and your new one looks factory 84. the only big difference i see is the choke. if you can find how to hook it up correctly, then it should work fine for ya

    are you gonna rebuilt both and keep one for a spare?
     
  7. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    where did you find this info?
     
  8. dyeager535

    dyeager535 1 ton status Premium Member

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    Not a lot of time to reply, but the chokes are different, ones electric (Yours I'm sure) ones hot air. You MIGHT be able to swap those two between the carbs. That additional vacuum line on the choke side is part of that.

    The other problem as was mentioned is EVAP.
     
  9. hi pinion

    hi pinion 3/4 ton status

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    Oh ,,,this is going to be a good thred, Stave, good job on the close up pics, i have the 85 carb, ill be watching and learning from this post ! :waytogo: :thumb:
     
  10. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Found http://www.recarbco.com/technical/rochester/qjet.html <---there, but it says on the bottom of the page that even Rochester didn't follow their own rules all the time. If the 2 had been a 5, they would be CA emmissions legal...
     
  11. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Oh dear... if my googling is accurate... your new carb (BHT) came off a V6 rather than a V8, which means much lower CFM... they ranged from 450-650 on the V6 Q-Jets if I'm not mistaken... The HTB is off a V8 (obviously)... which could be one of 700, 750, or 800 i think??

    From another message board...

    This would confirm the idea of the 78 carb (new one) could have been from a Cadillac V6... Though offhand, I can't think of a Caddy in the late 70s that had a V6...
     
  12. 77crewcab

    77crewcab 1/2 ton status

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    Are you able to post a listing of what the 3 letter designations are mine is 1914 HCD and I haven't been able to find any info for what it means. The main code states it is a 84 chevy auto carb.
     
  13. Cricket

    Cricket 3/4 ton status

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  14. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Only the first link you gave should have any bearing on the carbs we are discussing here... unless you are rebuilding a Pre-1976 Q-Jet... That's why I only posted the first link, because the other 2 links mattered not.

    As for the 3-letter code on the Q-Jets, I have not found any reference to them anywhere on the net... but I'm still looking, since I have a Q-Jet too...
     
  15. 84gmcjimmy

    84gmcjimmy 1 ton status

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    this is a kick in the jaw.
    So phenonix, if your right...it's off of a cadillac v6? yikes!
    I will look in my PM's to see if I had asked James where he got it from.

    What does EVAP stand for?
    So the old one is more technology advanced since it has electric choke?
    I will look in the book.

    I am just rebuilding one, the other one with be a wall hanging :grin:
     
  16. 84gmcjimmy

    84gmcjimmy 1 ton status

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    hope james doesn't mind if I quote this:
    from a PM:

    So I don't know.
    How can I know if parts will swap in between them?
    Thanks for the help guys
     
  17. Cricket

    Cricket 3/4 ton status

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    Go back and look more carefully, the second link also deals with 60's through 80's identification. Look in the upper right box, early 70 prefix and later 170 prefix are mentioned.

    The 3rd link is just a reference list for Steve or anyone interested enough to browse for misc non-specific information regarding Q-jets.
     
  18. dyeager535

    dyeager535 1 ton status Premium Member

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    The hot air choke carb being from a Cadillac makes sense.

    GM used the Q-jet on sixes WAY before the 80's, try 1960's firebirds with the straight six.

    They are either 750 or 800CFM that's it. But there are a few internals that changed, rods, jets, accelerator pump, power piston spring, and some more I'm sure I'm missing. That has to do with application.

    Don't sweat the original application. Run it, see how it works.
     
  19. 84gmcjimmy

    84gmcjimmy 1 ton status

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    So should I rebuild the "new" one, and swap parts from the old one if possible (electric choke?) and whatever else you guys suggest to make it more modernized? (sp?) Or what should I do? I'll be calling within the next few days after I find out what i'm doing...got to make sure they have the rebuild kit instock for my application.

    Thanks for the help.

    p.s. this is kind of a step ahead...but if I did put it on, and phenoix was right about the CFM, it won't wreck anything will it? What would it do, noises? Or just stall?

    Thanks, tonigght...i'm READING :)
     
  20. PhoenixZorn

    PhoenixZorn 1/2 ton status

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    Steve, I was wrong about the CFM on the Caddy carb... they were still 750 or 800 CFM, even on the V6... don't sweat it, it will work.
     

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