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Carb question

Discussion in 'The Garage' started by babyburb, Jan 16, 2007.

  1. babyburb

    babyburb 1/2 ton status

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    A little technicle know how needed. When I HAMMER on my gas, mainly from a stop, it hesitates if not dies out. If it does not die out it hesitates and then chuggs to get going. If I have some speed up and hammer down, the 4 barrel dumps and I go.
    I just had a mechanic rebuild my carb with a kit. I thought it was a bad accelerator pump but still doing it. He did say it did not come with the new pump but it did have a new rubber seal for it.

    Any Idears?

    Thanks for the Help.
     
  2. vortec

    vortec 1/2 ton status

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    how about timing? vac hoses? it's hard to get that mess of tubes routed right, without reliable diagrams.
     
  3. babyburb

    babyburb 1/2 ton status

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    My uncle is waiting on his timing light to come in and then I can check that. The vacuum lines, well, I dunno. Where can I get a diagram of these?
     
  4. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    Sounds like it may be going super lean when you punch the throttle. It probably needs some adjustment in the accelerator pump circuit. How was it adjusted? What carb?
     
  5. babyburb

    babyburb 1/2 ton status

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    not sure of the adjustment but it is a Rochester Quadrajet. I have the serial number at home and then I can tell you the model. We adjusted it to idle smooth in park, when I put it in gear in chugs a little but still runs pretty smooth. Other than that, the only time I have troubles is when it is stopped and I gas it. Any other time it dumps the four barrel and hauls tail. Does the carb kits usually have a new accelerator pump? This one just came with a new gasket.
     
  6. diesel4me

    diesel4me 1 ton status Premium Member

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    pump adjustment..

    On most Q-jets,the accelerator pump stroke is adjusted by bending the linkage..the carb kit should come with instructions and pictures,also a spec chart with the correct settings for it..you have to back out the idle speed screw until the primary butterflies are completely closed,before measuring the stroke..I've had a few carbs that needed a longer stroke than the specs called for,to accelerate properly..

    Good parts stores can get a new accelerator pump separately--standard-hygrade makes them,as well as many other brands..NAPA might stock some,but others will have to order one most likely..the "check ball" located in the carb body for the accelerator pump might not have been changed--if its rusty or pitted,the pump wont squirt good..dirt in the passages can plug them up too..or maybe the bore where the pump rides is scored or hogged out,that will reduce the amount of fuel delivered as well..

    It could also be the secondary air valve on the rear barrels is opening up too soon,causing a bog..that can be adjusted too,the directions in the carb kit should cover it..its difficult to explain how over the internet...:crazy:
     
  7. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    One thing you may try to see if it helps. Try richening up the idle mixture a little. Maybe an 1/8 turn on both screws. If it is leaning out, that may help a little. You could experiment and see if you can make any difference.
     
  8. 1977k5

    1977k5 3/4 ton status Vendor

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    If the carb seems to be running well everywhere except WOT, it is probably the secondary butterflies. There is a screw on the passenger side of the carb that is spring loaded and held down by a very small allen head bolt. The allen head bolt is kinda underneath the adjustment screw. Put a flathead screwdriver into the adjustment screw and hold it there (remember, this is spring loaded). Loosen the allen head bolt and tighten the adjustment screw 1/8 of a turn and retighten the allen head bolt. That should get rid of your problem :thumb:
     
  9. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    38377k5 would know, I've seen his truck run on the trail and his carb is set up great. At first I thought he had TBI. :wink1:
     
  10. dyeager535

    dyeager535 1 ton status Premium Member

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    IMO it is likely timing. Timing will make a HUGE difference on how well you accelerate from a stop. Not only timing BTDC, but if the advance mechanism inside is working right as well. May be sticky, worn, etc. Easy and worth checking.

    Accelerator pump is pretty easy to test: pump throttle with engine and air cleaner off, watch the squirt into the primaries. If it gets a good squirt, it's working.

    Accelerator pump is blamed for Q-jet problems (and wrong) as often as the ECM is blamed for problems in EFI applications in my approximation. They are exceedingly simple on the Q-jet.

    You don't really need a new accelerator pump piston, the seal is what pressurizes the fuel to squirt it out into the venturi's, and the whole assembly is simply a metal shaft with a spring and spring seat, with a gasket on the plastic piston end. If the spring is still springy, it's good. The carb body is what serves as the "cylinder" for the pump piston.
     
  11. 1977k5

    1977k5 3/4 ton status Vendor

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    It *could* be the timing but I still put my money on the secondaries. Worth checking both because both are easy to check.
     
  12. babyburb

    babyburb 1/2 ton status

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    thanks for the responses. I have pasted and copied all and will try to get to work on my truck ASAP. I will keep you posted.
    Thanks again.
     

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