Q-Jet too rich and leaking fuel

Discussion in 'The Venerable Q-Jet' started by dennisL, Aug 31, 2014.

  1. dennisL

    dennisL Member

    The car: 1970 Electra 225 Custom
    The carb: original 7040240 Quadrajet
    The problem: fuel leaking on top by the pump plunger, also dripping fuel on passenger side where primary shaft exits carb.

    The car sat for 15 years. After cleaning the gas tank, I thoroughly cleaned and rebuilt the carb using a Hygrade Jiffy rebuild kit. I set the float height to 3/8" as per Hygrade instructions. On start-up, the engine is WAY TOO rich and fuel comes out at the top front of carb by the pump plunger.

    So I take the carb apart and replace a few parts (obtained from Quadrajet Parts.com); needle and seat (.125"), and float (switched to brass). Start the car and the same thing happens again, way too rich and fuel at top front of carb.

    My "common sense" tells me that the float is too high but I don't know what measurement to use since its now at the recommended height of 3/8". The needle is not sticking and besides, I tried two of them: the one from the carb kit and now the .125 which is smaller.

    If this problem sounds familiar to anyone please tell me what it is. I'm anxious to get this car back on the road.

    Thanks,
    Dennis
     
  2. Pinder

    Pinder Well-Known Member

    I recently put a brand new carter fuel pump in. I have a Rochester Carb I rebuilt. It was running fine before i put the new fuel pump and it ran very rich and leaked gas around the bottom gasket. Car would run for a bit then flood. It was caused by new new fuelpump pressure being 8psi. Apprently Q jets dont like pressure more than 8psi because the float and needle wont be able to cut fuel off when bowl is full. Check fuel pressure of fuel pump. My problem went away when i put my old fuel pump back in.
     
  3. Pinder

    Pinder Well-Known Member

    Sorry I meant Q jets dont like pressure above 6 psi.
     
  4. carmantx

    carmantx Never Surrender

    Some questions.
    How are you measuring the float height?
    Get a good quality accelerator pump with garter spring. Toss the jiffy hygrade stuff. Poor quality.
    Did you make sure the needle and seat sealed at bottom? When you took out old needle seat, did you make sure the old gasket was pulled out? Many times they stick and are hard to remove. It needs to be removed so you don't have double gaskets. Also, the Needle/seat threads get corroded and need to be cleaned so new one will seat properly.
     
  5. dennisL

    dennisL Member

    I will test the fuel pressure. The fuel pump has been on the engine for awhile and about 30,000 miles. For a stock setup it should be what, 3 - 5 psi?

    I measured the float height as per spec: Push float down against needle, measure from top of casting to top of float at 3/16" from edge of float toe end.
    I then tested the needle by holding the carb upside down while holding the float rod in its slot. I put a rubber plug (that came with my vacuum tester) in the fuel inlet, blew into the plug's hole and could feel the resistance. Turned carb right-side up and repeated test, this time no resistance to air pressure.

    The accelerator pump is the one from the Hygrade kit. So I'll have to get a good one.

    I did get the old gasket out when I replaced the needle and seat. However, the new .125" needle was tighter than the old one and a little harder to screw in. I believe its seated properly but not 100% sure.

    So, to summarize I'll pull the carb off and check the needle again. I'll replace the accel. pump with a good one (any recommendation or is Quadrajet Parts.com a good source?)

    Anything else you can think of?
     
  6. carmantx

    carmantx Never Surrender

    Good parts can handle 8psi of fuel pressure.

    Cliffshighperformance.com or Quadrajetparts.com will have a good accelerator pump with garter spring, and whatever parts you need.

    Double check that needle/seat and make sure it is sealing at the base. Many of the ones I build have to have use a thread chaser to clean up the threads enough for it to seal properly. If upside down, it should seal solid, not just some resistance.

    Did you check to verify the check ball is seated? Lightly tap the old ball to make sure there isn't a rough edge to prevent it from sealing all the way.

    Last thing, maybe. Did you seal your well plugs? Most don't leak on the 70's and newer carbs, but some do. I always use marine epoxy to seal them.
     
  7. lemmy-67

    lemmy-67 Platinum Level Contributor

    +1 on the well plugs. If they are brass cups, those always leak. Your leakage from the primary shaft could be from there, however the fact you've got gas from the pump shaft indicates the float could be too high. Always use new floats when the rebuild is done...brass ones can leak and the foam ones can gain weight.
     
  8. techg8

    techg8 The BS GS

    another thing to check:

    be sure the "C" shaped float pivot isnt too flattened out.

    I have seen them somehow get flattened to where on a rebuild they dont get held in place by the air horn. this allows the fuel pressure to lift the needle, and float, and thus the pivot - which allows continuous fuel inlet flow.

    pull the "c" pivot out and use a large flat bladed screwdriver to open it up just a little til youre sure the air horn will hold it down in place.
     
  9. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The Q jet in my car now has absolutely no problem at all with 9 psi. I have seen my pressure occasionally spike to 10 or 11 psi, still no problem at all. It is a 7042240 last rebuilt by Jim Weise. My fuel pump is the CV products pump that I got from Jim when he built my current engine. It is rated at 8-9 psi.
     
  10. lemmy-67

    lemmy-67 Platinum Level Contributor

    +1 on this point too...this is the float hanger. When the bowl gasket is in place, it should push that hanger down totally flush in the slot with zero play. If there's any play, your float height adjustment will mean nothing and the needle will never push down with enough force to regulate the fuel flow.
     
  11. dennisL

    dennisL Member

    First I want to thank all that replied. You guys are awesome!

    Mark, I did epoxy the well plugs even though there was no evidence of leaking. Today I lightly taped the old check ball then replaced with new one. (I didn't do that during the last rebuild.) Using a thread chaser on the seat threads was a great tip and I just did that. Now the seat screws in nice and smooth and its easy to tell when it is seated tightly. Oh, and with the needle - seat closed I could not blow air past it. I described it as "resistance" but I meant that it was closed. Thanks for the advice.

    Ken G, I just bent the "C" float hanger for a tighter fit. I put a metal ruler on the top of the fuel bowl casting (where the gasket would normally be) and initially I could lift the hanger a little before it hit the ruler. Now it cannot be lifted, nor does it stick up above the casting top surface.

    I ordered a new accel. pump and return spring. The garter spring and new cup material is definitely what I should have.
    I haven't measured fuel pressure yet as I have to rig up some adapters to mate the 3/8" hard line to my gauge, but I will.
    Again, thank you all for the help. I'll post the results when the carb goes back on the engine. (I'm now saying a prayer to Saint Rochester, the patron saint of Quadrajets.)
    Dennis
     
  12. dennisL

    dennisL Member

    Since I started this thread, I thought it appropriate to post the results. The carb is back on and I'm pleased to say that the fuel is now staying inside the carb, with the outside totally dry.

    As suggested here, I tested the fuel pressure and found it to be 5 - 7 psi while cranking. Since this is normal I then tested the new float and needle & seat with both air and fuel pressure, it passed. So then I installed the air horn together with my new "garter spring, blue cup" accelerator pump and put the carb back on the engine.

    What actually fixed the problem? Since I replaced multiple parts, I'm not exactly sure. I did discover that the air horn is warped slightly at the front. Exactly where the ridge is that applies pressure to the float hanger. So I compensated by raising (opening) the float hanger just a "tad". I don't know, maybe 1/32". The tricky part was getting the hanger bent to exactly the right height. If too high, it would prevent the air horn and gasket from sealing. If too low, the needle would not seat/close. My theory is the float hanger was not bent open enough and causing a fuel "overflow".

    So its all good and again, thank you for taking the time to help get an old Buick back on the road. I couldn't have done this without your help.

    Dennis
     
  13. Pinder

    Pinder Well-Known Member

    This is good info. Maybe I need to take my Qudrajet apart again and check the stuff you did. Right now its running fine with my old fuel pump. But the New one had 8psi and it overflows my Q jet. Im thinking of maybe upgrading to electric pump as my old pump has a ticking sound to it.
     

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