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Why does this happen?

Discussion in 'The Garage' started by American84K5, Mar 11, 2005.

  1. American84K5

    American84K5 1/2 ton status

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    Some times when i open it up to all 4 barrles it dies... like the other day i tried to spin the tires and it dies... why does this happen?
     
  2. wraenking

    wraenking 1/2 ton status

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    do you have a rear float adjustment?

    if you do, i think you need to adjust it at a higher rpm.

    just a stab. see what the pros think
     
  3. Beast388

    Beast388 1/2 ton status

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    What kind of carburetor? What are your engine specs?
     
  4. Jonny-K5

    Jonny-K5 1/2 ton status

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    carb needs adjusting. probly the stock Qjet. your probly better off taking the truck to a carb shop and giving them a 50 to tune it. or they'll tell you it need rebuilt. carbs are tricky, and since it sounds like you dont have much experience w/ them , better off leaving it to the pros. just my .02 tho.
     
  5. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    The infamous Q-jet bog...

    If you're lucky Dorian will see this thread and reply, he is pretty knowledgable with those things.

    Rene
     
  6. American84K5

    American84K5 1/2 ton status

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    4 barrel off some 80s model gm truck... 350ci engine bored .030 over,small valve 305 heads
     
  7. dyeager535

    dyeager535 1 ton status Premium Member

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    Have you played with your timing at all?

    You can get a FIERCE bog (enough to kill engine, not sure) if your timing is wrong for the setup just a bit. If you ease into the throttle, or at least get it rolling before stabbing throttle, do you still notice it?

    305 heads would make me think that perhaps you do have a timing issue.

    If you can stab throttle in other conditions (cruise, rolling, etc) and not have the engine die/stumble I would not suspect the accelerator pump.
     
  8. BlueBlazer

    BlueBlazer 1/2 ton status

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    Assuming this is a Q jet, tighten up the secondary air valve spring. What it likely happening to you is when you go to WOT, the secondary air valve, which is controlled by vacuum and spring pressure acting against each other, is opening too quickly which instantly leans out your mixture and causes the bog. Slowing the rate of air valve opening should help this. It is an easy adjustment that you can play around with until you get a nice crisp throttle response.
     
  9. American84K5

    American84K5 1/2 ton status

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    thx,
    not at all... all ideling around 700
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    What do you mean? You are running higher compression than the system originally was designed for, and different heads with a different chamber than original.

    700RPM means?
     
  11. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    I think maybe he's using "idle speed" interchangably with "timing".... :blush:

    A84K5,

    Timing an engine requires a timing light that measures how far ahead of TDC (top dead center) the plugs are fired. The amount of "advance" (which is measured in degrees) is what Dorian is asking about....

    Typically you will need to know the advance at idle, and at some higher number (called total advance) since the amount of ignition timing will increase at higher RPM.....knowing at what RPM the timing is "all in" is another piece of data that will help understand how to diagnose your problems.


    :cool1:
     

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