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Tuning a Q-Jet???

Discussion in 'The Garage' started by MaxCrack, Oct 3, 2003.

  1. MaxCrack

    MaxCrack 1/2 ton status

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    Where do I start. I didn't even want to rebuild it because of my lack of knowledge about the thing. But I had to. And now it is running really rich. So, where do I start? /forums/images/graemlins/1zhelp.gif
     
  2. Okiemuddog

    Okiemuddog 1/2 ton status

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    IIRC you should turn each one of the idle mixture screws on the base. Start with one side, turn it in until the engine starts to run rough then back it out until the engine smooths out, then turn it another quarter turn out and move to the other side. might have to do it a couple of times to get it just right. FYI, check your plugs and timming they will also cause the same problem /forums/images/graemlins/thumb.gif
    Q-jets are cake to rebuild, just make sure to note where everything came out from


    Krennen
     
  3. MaxCrack

    MaxCrack 1/2 ton status

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    Heheh, there's my problem. I did just rebuild it. No problem. But since I rebuilt it, it has been running very rich. Idle mixture screws are now all the way in, as lean as possible and it still idles high. Timing did not change, since rebuilding the carb. Only thing that changed is the carb. It got thoroughly cleaned and new parts. How do I lean it out across the board. From idle to full throttle?
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Did you mess with the choke? Is it fully open when the truck is warm?

    Is the timing and idle speed correct? All bolts/screws etc. tight?

    If all of those check out ok, sounds like you might have a mal-adjusted float, or a sticky power piston or related.

    Just my opinion.
     
  5. boz42

    boz42 1/2 ton status GMOTM Winner

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    check out the book Rochester by Doug Roe. it is published by HP Books. i just got a copy this week-end, all the speed freeks say it is an excellent source for Quadra-Jet info.
     
  6. Thunder

    Thunder 3/4 ton status

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  7. Goober

    Goober 1/2 ton status

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    [ QUOTE ]
    Idle mixture screws are now all the way in, ... and it still idles high

    [/ QUOTE ]

    Fuel is dumping from somewhere. Are you sure you used the correct gaskets? Most rebuild kits come with a few different ones and they all appear to be pretty similar. If the wrong one gets used then you end up with vacuum leaks all over the place.


    [ QUOTE ]
    as lean as possible

    [/ QUOTE ]

    If you setup Quadrajet idle circuits too lean then they will act and smell like they are running rich. This is because the air/fuel mixture doesn't ignite in the cylinder, the engine will start to miss and raw fuel dumps out the back.


    My guess is that something was overlooked when you put it back together. No big deal. I've rebuilt a truckload of Quadrajets and I still goof up sometimes. Just take it apart and doublecheck your work. Make sure you don't have any vacuum leaks and give it another try.


    Doug Roe's book is BY FAR the best book available for Quadrajet information. It will pay for itself quickly.


    Have fun! /forums/images/graemlins/thumb.gif /forums/images/graemlins/thumb.gif
     

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