AF: Carb "sucking air" when I tap the gas to downshift while doubl | Allpar Forums
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Carb "sucking air" when I tap the gas to downshift while doubl

Discussion in 'Repairs, Maintenance, Help' started by power_wagon53, Feb 16, 2014.

  1. power_wagon53

    power_wagon53 New Member

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    Recently my dad and I got our '49 dodge b1b running. It runs great I am just having problems on acceleration and when I need to tap the gas for downshifting. Instead of shooting gas and increasing the rpms, I hit the gas and all I get is a quick suction of air through the carb and don't get the necessary amount of gas in order to rev match like it should. If it is sitting at an idle and I mash the gas, the same thing happens and it almost dies on me. I'm assuming this is a carb problem, but I really have no idea exactly what I'm looking for. Any help would be appreciated, trying to get this this back to beautiful little by little for my dad.
     
  2. ImperialCrown

    ImperialCrown Moderator
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    Welcome to Allpar. The accelerator pump may be damaged, worn or inoperative. Older vehicles used a leather pump cup that could dry out and shrink if the vehicle sat. Newer vehicles used a Viton rubber cup which lived longer. You may need to find a carburetor rebuild kit to refresh the seals and gaskets.
    Carter or Stromberg? Do you have a service manual or know the carburetor model #?
    0900c152800553a6.jpg
     
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  3. power_wagon53

    power_wagon53 New Member

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    It's a carter that was rebuilt maybe 4 or 5 years ago. This truck was/is part of an ongoing restoration project and within that 4 to 5 year range, it did a lot of sitting so is it safe to assume that this could cause the accelerator pump some grief? . I'll look into the accelerator pump and yeah we have a shop manual and the model #. Thanks a bunch!
     
  4. ImperialCrown

    ImperialCrown Moderator
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    What Carter model?
    This is a diagram of a 'generic' accelerator pump system. It may not be yours, but the idea should be similar:
    fig0422.gif
    First, the pump cup has to seal well in order to give a good fuel squirt. When they dry out, they can shrink.
    Then the check ball has to be there. I have seen check balls mistakenly left out after a carb service.
     
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  5. power_wagon53

    power_wagon53 New Member

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    [​IMG] Hopefully this picture shows up, sorry or the long delay, college is a busy time for me. [​IMG]

    Referring to thepicture, I'm not sure what type of carb it is. If you could help that what be great.
     
  6. dana44

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    Agree. If the accelerator pump itself isn't the culprit, then there is a plugged up passage from the accelerator pump to the squirter. That you can test by looking down the throat of the carb, hit the throttle and see if there is fuel squirting from the little squirter. If not, rebuild.
     
  7. 68RT

    68RT Well-Known Member

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  8. ImperialCrown

    ImperialCrown Moderator
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    It does appear to be a Carter BBS (Ball&Ball Single).
    The model # is stamped into a tag fastened under a float cover screw head that may be long gone.
    It should also be cast into the flange base or float body assembly.
    It may be 3 numbers followed by the letter 'S' or a 'letter-number-letter-number' model ID.
     
  9. 68RT

    68RT Well-Known Member

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    Also, make sure the heat riser is working but that should not affect the engine when hot.
     
  10. power_wagon53

    power_wagon53 New Member

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    So we just recently got the truck back from a mechanic who replaced the accelerator pump while he was working on other things. After it returned home I took it for a drive and now the issue is worse than ever, almost to the point that it can't be driven. So i figured if a mechanic couldn't see what the problem was, I might as well take a look myself. Opened up the carb and yes the accelerator pump had been replaced, but there was quite of bit of rusty sediment below the float bowl and beneath the accelerator pump. I was wondering if this could cause such a dramatic response? gas is still squirting from the squirter thingy.
     
  11. tazdevil

    tazdevil Member

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    That crud has likely plugged the pump orifice and probably the jets. Time for a good soak in cleaner and all new gaskets and pump plunger.
     
  12. ImperialCrown

    ImperialCrown Moderator
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    There should also be an inlet check-ball so the squirt goes out the nozzle and not back into the float bowl.
    The external pump rod must be adjusted correctly.
    Sediment must be cleaned out of the carb bowl and passages. Add a fuel filter if necessary. Is the sediment bowl/pressure regulator at the carb inlet catching any debris?
    Dwell and ign timing must also be in spec.
     
  13. power_wagon53

    power_wagon53 New Member

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    Inlet check ball seems good, I'm getting a good squirt. After giving it a good cleaning and re-installing, and then re-re-installing after it started leaking profusely from God knows where, acceleration problem still exists. As I was taking a look at the guts, I was looking at the spring for the accelerator pump, being new to these I was wondering how much of a gap is there between the top of (not sure of the terminology) arm attached to the plate with three holes in it and the top of the spring on the accelerator pump. When I move the throttle to open it doesn't seem to push the pump down hardly at all because there is such a big gap. Is this normal? I checked an old b&b lying around and it appeared the same so I'm not sure. I will try and have some pictures of what I'm talking about tomorrow.
     
  14. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    If you get a good steady squirt from the pump, then that part's OK.
    Another thing that can cause this problem when driving is if the float level is too low. I don't think it particularly affects throttle response when parked. But if the float is low, it will sound like it sucks air when you get on the gas, then as you let up, it will recover and lunge forward a little.
    Is the gas leak fixed now?
     
  15. JTE

    JTE Well-Known Member

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    How does the timing advance on that truck?
    A vacuum leak through the diaphragm would appear as a stumble.
     
  16. power_wagon53

    power_wagon53 New Member

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    I dont know if these pictures help, but they show the full range of motion of the arm that's supposed to push on the accelerator pump. As noted before it maybe presses it down 1/8th of inch, maybe. Is it supposed to push it down more? the little arm thingy is set in the middle hole of the three.
     

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    #16 power_wagon53, Mar 11, 2015
    Last edited: Mar 11, 2015
  17. chuzz

    chuzz Well-Known Member

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    I'm more inclined to go with Bob on this one. It's been years since I had a flat head six, but the float level is critical on these engines. Who rebuilt the carb for you or was it a DIY? If so, did the kit you used come with a float gauge for you to set the level and drop with? If not, it's pretty much a guessing game.
     
  18. Bob Lincoln

    Bob Lincoln "CHECK FAULT CODES"
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    Float level MUST be set within less than 1/16 of an inch of spec, to run properly - in my experience.
     
  19. 68RT

    68RT Well-Known Member

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    Here is some info. The picture showing the height of the accelerator plunger looks like it is stuck in the up position. When the Throttle is opened, the lever goes down and allows the spring to push the plunger down causing the stream to be pushed at a controlled rate through the pump nozzle. The "T" at the top is to pull the plunger back up when the throttle is closed to prepare for the next opening. Second link is the Carter overhaul manual. The first should have your settings.

    http://www.allpar.com/fix/fuel/carter-BB.html

    http://c809017.r17.cf2.rackcdn.com/carter_bb_manual_1939_later.pdf
     
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  20. ImperialCrown

    ImperialCrown Moderator
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    It does sound like it is lean when the throttle opens. A healthy squirt from the accelerator pump makes me think that the pump is OK.
    Does this carb have a power metering valve?
     

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