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Technical Quadrajet carb

Discussion in 'The Hokey Ass Message Board' started by coolieman, Nov 7, 2019.

  1. coolieman
    Joined: Jan 31, 2010
    Posts: 134

    coolieman
    Member

    I have a 327 chevy 4 barrel carb. New mechanical fuel pump, I have a clear gas filter and after it sits a couple weeks the filter goes dry. I know the pump is supposed to have a check valve but I didn't think it was doing its job, so I installed a one way valve in fuel line to keep gas from running back to pump . My question is will this keep to much pressure on carb and cause it to flood. I drove it around some and carb started flooding took it off still flooded so I replaced float needle seat doesn't flood now but would like to put valve back in line . I don't know if that was a coincidence or not , thanks mike
     
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 51,160

    squirrel
    Member

    If the one way valve in the pump is not working, it will not pump. I don't think you need to add another valve.

    Modern gasoline evaporates rather quickly. If I don't drive my cars every day or two, the fuel evaporates out of the carb, and I have to crank it a while to get it going again. That's with everything working as it should.
     
  3. Mike VV
    Joined: Sep 28, 2010
    Posts: 2,596

    Mike VV
    Member
    from SoCal

    What squirrel said.
    Just todays gas. All carbureted, mechanical fuel pump engines have the same problem.
    If you want to alleviate the problem, an electric fuel pump is the answer. Turn the pump on for a few seconds before turning the key, all should be fine.

    Mike
     
    AHotRod likes this.
  4. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 4,060

    2OLD2FAST
    Member
    from illinois

    Q-jets are notorious for percolating after being shut off , especially if the intake is carboned up and/ or the base gaskets are wrong application or damaged ...
     
    RMR&C and dirty old man like this.

  5. DOCTOR SATAN
    Joined: Mar 21, 2014
    Posts: 711

    DOCTOR SATAN
    Member
    from okc

    Tighten the hose clamps....maybe new hose also
     
  6. carbking
    Joined: Dec 20, 2008
    Posts: 3,310

    carbking
    Member

    AHotRod and j-jock like this.
  7. You may have gotten some debris in the carb side of the filter that caused a temporary issue.
     
  8. I had the same issue with the fuel evaporating, and that plus having a Qjet with an internal leak (fixed), made it a true pain in the butt to start after the truck had been sitting for a week or more. I installed an electrical pump between the tank and the mechanical pump.
    This solved the problem.
    Bob
     
  9. The engine should still start right up if the float bowl is full. Q jets had a problem with the soft plugs in the bottom of the bowl would leak and the bowl would drain all fuel if the car sat for a time. If the the bowl is empty after sitting I would suspect those plugs. You used to be able to buy rubber plugs that went between the bowl and the base plate that prevented the leak. The other fix is to clean and seal the plugs with epoxy.
     
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  10. coolieman
    Joined: Jan 31, 2010
    Posts: 134

    coolieman
    Member

    What make model pump did you use and do you leave it running and does mechanical pump still pull gas thru thanks mike
     
  11. doug3968
    Joined: Sep 13, 2014
    Posts: 38

    doug3968
    Member





    Sent from my iPad using The H.A.M.B. mobile app
     
  12. doug3968
    Joined: Sep 13, 2014
    Posts: 38

    doug3968
    Member

    Hot Rod mag recently had article re: fixing dribbling Qjets with kit from Ohio shop. Also fix for throttle plate wobble.





    Sent from my iPad using The H.A.M.B. mobile app
     
  13. lostone
    Joined: Oct 13, 2013
    Posts: 2,028

    lostone
    Member
    from kansas

    Yeah sounds like well plugs leaking. Quick fix? Get a little toothbrush style wire brush and jb weld. Pull bottom plate off carb, use wire brush to clean the crap out of the plugs then some carb cleaner, let dry good and then mix up some jb weld and cover the plugs really well.

    One thing to be careful of is using too much. So after coating the plugs wait about 5 minutes and try putting the bottom plate on, make sure that the jb weld isnt to thick to allow the plate to seal.

    If all checks out let it set over night and put back together the next day and enjoy... One note, after you do this you can throw the stupid foam "seal" away that comes in kits for the well plugs.
     
  14. manyolcars
    Joined: Mar 30, 2001
    Posts: 8,696

    manyolcars

    One guy wondered where the gas was going so he set the carb on the bench, filled it up, came out the next morning and the crap gas they sell us had evaporated
     
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  15. AHotRod likes this.
  16. garyf
    Joined: Aug 11, 2006
    Posts: 250

    garyf
    Member

    They do make a paper fuel filter with a check valve built in, for the inside of the carb . Make sure you have the spring behind the filter. They worked keeping the bowl from emptying before ethanol was around.
     
    Last edited: Nov 7, 2019
  17. I bought the electric pulse type pump on ebay. It is a solid state unit, and I have also been running the same pump on my excavator with no issues.
    I am using the pump to feed the mechanical pump, and the setup is working great. After the truck has not been used for a couple of weeks, all I have to do, is turn the ignition on, count to ten, and everything is primed and ready to go.
    If the electrical pump was to fail, the mechanical pump will pull just fine. I tested this, my having the electrical pump plumbed into the circuit and disconnected the power. There were no issues with starting or driving, even at full power.
    Bob
     
  18. coolieman
    Joined: Jan 31, 2010
    Posts: 134

    coolieman
    Member

     
  19. My vote is also evaporation, sometimes we look for a problem when there isn’t one. I have the same issue if I don’t drive them every day or two as well, just like squirrel said. I just know it’s going to crank awhile.


    Sent from my iPhone using H.A.M.B.
     
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  20. Vimtage Iron
    Joined: Feb 28, 2010
    Posts: 554

    Vimtage Iron
    Member

    If your plumbing the electric thru the mechanical one and using it full time there is a possibility of the diaphram cracking on the mech pump and the electric filling the crankcase with gas, this is not a pretty picture.
     
  21. I agree that what you state is possible, but it is not probable.
    The mechanical pump is fairly new, and the pulse pump is not a high pressure pump. I haven't checked the pressure of the electric pump myself, but I am not concerned.
    Bob
     
  22. I have electric pump in back and SBC with mechanical pump. I have a manual switch on electric pump.
    When car has not been started for four or five days, I switch on electric pump. Wait a few seconds. Click the auto choke on by touching accelerator oecal. Start cranking. Usually fires in less than ten seconds.
    Once it is started I turn electric pump off and run on mechanical pump.
    Occasionally I get a vapor lock stall on the highway. Switch on electric pump and it restarts itself. Might then have to leave electric pump turned on until next scheduled stop.
    I try not to overwork electric pump. Carter 4070.

    Phil
     
    j-jock likes this.
  23. Good idea, I will do the same, because the only thing I am really using the electric pump for, is for the first cold startup. The rest of the time, the engine fires up immediately.
    I don't know why I didn't think of it, because that is the exact setup I have on my plane, a Lake amphibian.
    Bob
     
    pprather likes this.
  24. I believe I have the electric pump on a circuit with a ten amp fuse. The toggle switch I believe is rated somewhere above 20 amps. Also have one of those plastic flip covers on the switch.

    Phil
     
  25. coolieman
    Joined: Jan 31, 2010
    Posts: 134

    coolieman
    Member

    Thanks for all of the replys , one thing that has not been Addressed that was asked in my original post is [ will the inline 1 way valve hold to much pressure at the carb] it is between the carb and pump which keeps fuel filter full when engine is not running . Which keeps carb primed
     
  26. It's not possible to keep the carb primed with today's oxygenated fuel. The fuel evaporates much more quickly than anyone would think. That's why the carb needs to be re-primed if it sits for a few days.
    Unlike a mostly air sealed efi system, most of the carb internals are open to the air.

    Phil
     

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