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Quadrajet help

Discussion in 'The Hokey Ass Message Board' started by BaBa, Jun 17, 2013.

  1. BaBa
    Joined: Jun 2, 2011
    Posts: 114


    The Quadrjet in my PU (originally from 74 Camaro) bogs and hiccups when you get into the secondaries. It seems to run fine on the primaries. Can you think of something minor this may be and how would I check? I'm thinking either accelerator pump or the vac isn't working on the secondaries properly.
    Do you think I should rebuild, send out for rebuild or send out for tuning and rebuild?
    Do you have anyone that you would recommend for the rebuild and/or tuning?
    Thanks for any input!
  2. Normal Norman
    Joined: Aug 9, 2006
    Posts: 510

    Normal Norman
    from Goshen IN.

    I'm not a Q/J lover, I would toss it in the trash and slap on a nice holly and be done with that struggle. N.N.
  3. rustednutz
    Joined: Nov 20, 2010
    Posts: 1,580

    from tulsa, ok

    Quadrajets are fine when they work right. They generally give you good cruise fuel mileage because of the small primaries. However they are one of the tougher carbs to get working right. I'd buy the correct kit, do a rebuild by soaking the disassembled carb in a good carb cleaner, blow out all passages then pay attention to the many adjustments neccessary to make them work. The secondary air valve adjustment is probably not set correctly causing the secodaries to open too quickly before there is enough vaccuum to draw fuel into the secondaries causing a lean bog.
  4. hoop98
    Joined: Jan 23, 2013
    Posts: 1,362

    from Texas

    Two known problems.

    The Vacuum Break (The gold cannister),choke pull-off also brakes the Air Valve opening. If the diaphragm is shot they will just flop open.


    Also there can be a problem with the cam that raises the metering rods.

    Probably just a simple rebuild but there are a number of recognized experts if you want to go that route.

    Link to a rebuild

    Bob Jennings Dynotune
    North Hills, CA

    The Carb Shop (Vrbancic Bros. Racing)
    Ontario, CA

  5. Bryan G
    Joined: Mar 15, 2011
    Posts: 188

    Bryan G
    from Delmarva

    And I never had any luck with a Holley. Quadrajet can be an excellent carb, if you can only find somebody willing to work on them. Locally I found a guy who worked at a Chevy dealer in the 70s and he has a pretty good feel for 'em.
  6. 325w
    Joined: Feb 18, 2008
    Posts: 5,648


    Www. Cliffs quadrajets. They sell brass floats inlet/filter repair fittings. Nice folks. Do great work.
    Last edited: Jun 17, 2013
  7. Yep! Before you dig into a rebuild, give this a try. Pretty easy to adjust and can make a world of difference! :cool:
    Joined: Jan 1, 2008
    Posts: 1,371

    from Bordertown

    Do yourself a favor and get a book on them. Its a truly amazing and very tuneable carb. I love'em. They can be quirky, especially with big cams. Ive had great luck with them, a book and a rebuild and you might become a believer as well. I will post up the book i have this evening.
  9. mt shasta steve
    Joined: Mar 26, 2010
    Posts: 270

    mt shasta steve

    My first thought would be accelerator pump. Easy to check by looking down the throat and racking the throttle. Maybe I'm jusy lazy, but I like to try the easy stuff first.
  10. deeddude
    Joined: Aug 30, 2011
    Posts: 127


    rustednutz has the advise that you should look into first. 9 out of 10 times this is the problem. I've seen people take the secondary air valve adjustment off only to discover that now their carb is junk. Once that's adjusted properly and you still have a problem seek out a rebuilder or buy Doug Rowe's book on QJ's. Awesome carbs and easy to rebuild.

  11. With the engine warmed up and the choke open, idling, take off the air cleaner and push on the secondary air valve. It should open with some resistance then snap closed. If it opens easily it needs to be adjusted. Shut off the engine. Under the right side of the air valve arm is an allen head screw and a small screw driver slot. Holding the screw driver in place slowly back off the allen screw, tighten 1/4 turn (to start) on the screwdriver (you will feel tension), hold it in place and tighten the allen screw. Drive it....reset as necessary...9 times out of 10 it is too loose...There are other things that can be done to a quad to make it run strong.
  12. rouye56wingnut
    Joined: Jan 14, 2008
    Posts: 352

    from mn.

    Most of the time the problem is a loose spring on the secondary air flap .If you first take your finger and tickle the flap and see if there is spring tension enough too cause some resistance to opening .If cou can easily flop it open , or sometimes it even will sort of stay open , then you need to tighten the spring .

    To do this on the end of the air flap shaft that the vacume break is on , you will see a small screw that is your adjuster . To adjust more tension . you first have to take a small allen wrench and loosen the jamb screw located under the plate . Then just dial in enough tention so that the flapper doesn't dump open so quickly and retighten the set screw .

    For those of you that never took the time to learn these , you are missing out on one if not the best running and fuel efficient carbs ever made . To mask your problem with installing an adapter and putting in place a (controlled fuel leak) Holley you are missing the boat .

    I see the response above got in as I was typing .As you can see this is well known about these carbs .
  13. carbking
    Joined: Dec 20, 2008
    Posts: 3,158


    The most common cause of the symptoms described is a fatigued secondary airvalve spring (assuming the spring is properly adjusted). This is a part that SHOULD be in ALL Q-Jet rebuilding kits; but is generally only found in the better kits. A defective choke pull-off will also cause issues, but the choke pull-offs are generally longer lasting than the spring.

    If you want the job done professionally, Cliff Ruggles would be my recommendation. Use the search engine of your choice and search for Cliff's High Performance.

    Cliff also wrote an excellent book on modifying Q-Jets for high performance work.

    (Opinion) The Q-Jet is an excellent carburetor for a street vehicle or for straight line racing. Those that throw rocks at the Q-Jet have either: (A) never applied themselves to learning about it, or (B) own stock in the oil companies.

  14. Larry T
    Joined: Nov 24, 2004
    Posts: 7,675

    Larry T

    The setting on the secopndary spring is usually 3/4 turn past enough tension to shut the butterflies. But that's not gonna completely fix the problem if the vaccum control for the butterflies isn't working. Or the cam that lifts the secondary metering rods is worn out, broken or gone.
  15. BaBa
    Joined: Jun 2, 2011
    Posts: 114


    Wow! You guys are a great resource. That's why I hang around here. OK I'll check on a few of the suggested adjustments and if those don't solve the problem I'll probably send it off to one of the experts and get it tuned to my engine's specifications and professionally rebuilt.
    I'm not afraid of rolling up my sleeves but the price of a rebuild kit and a few extra parts is about half the price of having a professional do the work and it will be fixed right.
  16. hoop98
    Joined: Jan 23, 2013
    Posts: 1,362

    from Texas

    I guess everyone's experience is a little different.

    The PRE-SFI Quadrajet Turbo Regal 3.8 was our most finicky calibration. There were huge variations in performance of the cars we got in. We started using a test-track to time them 0-55. A good one would do it in 5.3, bad ones were as slow as low 8s.

    We couldn't get much better than 5.1 with the Carb but we could get all the slow one's up to or rather down to low 5s.

    It all revolved around tuning the Secondary air Valve, mostly opening angle, this application liked then to line up with the edge of the vertical plates.

    That angle controlled the height of the metering rods, they typically went too rich when the air valve went full vertical or leaned out when they didn't open enuf. We drilled and tapped the stop and made them adjustable.

    Now back to different people having different experience. I'm not sure how many Q-Jets I worked on but it was mid 4 figures, literally thousands.

    I had hundreds of Vacuum breaks, dozens of metering rod cam related problems, and a handful of Secondary Air Spring problems, although we always checked them.

    That's just the way it broke out for me in Houston for 14 years.

    Of course now those carbs are 30 - 50 years old now so fatigue would be more of an issue.

    Virtually every vacuum operated device under the hood failed at a high rate, pull-offs, Vac Advance- Purge Valves the highest.

    Goes without saying you check it all and the most likely problem will be whatever you can't find easily.
  17. For big cams get Cliff Ruggles book and use the #2 or 3 recipe in the high perf/racing section.
  18. bobkatrods
    Joined: Sep 22, 2008
    Posts: 693

    from aledo tx

    X2 on cliff ruggles, use his kits and advise, most of the people who hate q jets just do not know how to work on them, THEY are a great carb when done RIGHT.
  19. the big Q is so under rated its funny. there is alot of power in one shave the pump and get a better shot of gas. there not as hard as thought 2 things to do 1 seal the fuel well and 2 bore the blades and use new shaft bushings its a must !
  20. so correct:eek:
  21. hoop98
    Joined: Jan 23, 2013
    Posts: 1,362

    from Texas

    Agree, bought the book just to read and bring back memories!!!!
  22. SeanRupp
    Joined: Jun 17, 2013
    Posts: 3

    from Ohio

    Cliff is a great resource for parts, the book he wrote on them and you can just call him and ask questions. I use a modified q jet on my 540hp roadrace pontiac and with a little re drilling of air bleeds and the right parts it works great.

    I was having a simular issue on my boats q-jet last season when i kicked it down and cliff sent me a new white accelerator pump diaphram, the old black one did not like the alcohol in the fuel as was not giving it the full shot of fuel when I stabbed the throttle.

    There are 2 books on q jets I have, the one is a dictionary sized manual by the guy who designed it and cliffs book is a 1/2" thick tuner guide much easier to understand and work from.
  23. BigDogSS
    Joined: Jan 8, 2009
    Posts: 912

    from SoCal

    Sean Murphy is the guy, IMO -->
    I had my first QJet built by the Carb Shop in Ontario, but they could not get rid of the off-idle, tip-in stumble. I even took the car to them. It wasn't bad, just annoying. I sold that car, but not because of the carb..
    My next car, I immediately sent the QJet to Sean with my specs and it came back spot on! The carb has been on the car at least 8 years with no problems.
    Several years back, CarCraft Magazine stated that the QJet carburetor was the next best thing to EFI.
  24. big M
    Joined: Mar 22, 2010
    Posts: 709

    big M

    Debris and sediment in the float bowl can partially plug the jets and cause these problems also. I agree with most others on this thread that the Quadrajet carb is well engineered, but problems arise when people unfamiliar with their workings open them up.

  25. hoop98
    Joined: Jan 23, 2013
    Posts: 1,362

    from Texas

    I had a 72 Torino 351 CJ with a Spreadbore Motorcraft.


    Had to use a Q-Jet to Holley adapter and modify it to the spread-bore throttle plates,

    On the weekends and at the strip I ran the Motorcraft but during the rest of the time it had a Q-Jet, remember this was around the first gas crisis and going from 10 - 13 MPG was big bucks.

    So just saying, you can work wonders with a Q-Jet on most any engine. IMHO
    BTW if it says Manufactured by Carter for Rochester, I'd try another. I never liked the Carter Built Q-Jets, we only had them on the Chevy 4bbl engines when they started the engine incest in he 77's
  26. Bad Eye Bill
    Joined: Sep 1, 2010
    Posts: 841

    Bad Eye Bill
    from NB Canada

    They weren't called Quadrabogs for nothin'. If you can find a guy who knows them and can make them work, they're a damn good carb.
  27. hoop98
    Joined: Jan 23, 2013
    Posts: 1,362

    from Texas

    I always thought Holleys were an awesome carb to have, if you were seriously upside down in your car but well insured. j/k :)
  28. I have mixed luck rebuilding Q-Jets, so I either bring it to a local rebuilder or buy a new one. Carter was re-popping them years back and they worked great.

    The last one I had done up ran me $250 with the option to bring the car back after I installed it and they'd tune it for me.

  29. 68vette
    Joined: Jul 28, 2009
    Posts: 306


    My corvette has had the present one on it now since 1984 without the first screw being turned....

    Just go to utube and type in 1968 corvette sunday drive....its the blue one.
  30. Sounds like everything is covered already. I'll jump on the "it's a great carb" boat, best of both worlds (performance and economy). I used to go to the pick a parts and pull the secondary hangers and metering rods off of junk carbs (broken cases), now I have a bag full and a few main jets.

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