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Another Quadrajet Question

Discussion in 'The Garage' started by jrpeebles, Apr 26, 2005.

  1. jrpeebles

    jrpeebles Registered Member

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    I recently replaced my Edelbrock with a Quadrajet.It fired right up and idled perfectly.Once the choke kicked open, I opened up the throttle and as the secondaries opened it backfired through tne carb. From this point on the secondaries have not opened.Is it possible that some components of the carb were damaged?I have not had time to pull the carb to take a look yet.Does anyone have any ideas/suggestions?Thanks in advance.
     
  2. g_mo

    g_mo 1/2 ton status

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    if your trying to get them to open while idling it aint going to work. qjets secondaries wont open at idle.
     
  3. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Backfiring shouldn't damage it , it has NO power valve . You would have to rev that thing pretty high to open the secondaries , that carb works on engine need , the secondaries really open as needed based on airflow .

    What you could of done is something with hoses , like your vacuum advance to the wrong port . Or ya could of gotten a plugwire in the wrong spot , assuming you messed with anything else while you were in there .
     
  4. K5Jocky

    K5Jocky Newbie

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    Back fire is ingnition or timing .Secondarys are Vac operated .you can remove top of carb and flip over in 1 of the corners of secondarys is a allen screw that adjusts spring tention allowing you to adjust whe they open.IE early Mid range or late I like early love to hear that mone
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    Agree on ignition or timing. Always solved my Q-jet backfires by timing the engine where it wanted timing.

    Most Q-jet secondaries are held SHUT with engine vacuum. No matter how light you set the tension with the spring on the passenger side of the carb, under no load (IE in park in your driveway) engine vacuum will STAY too high to allow the secondary vacuum break to back off from holding the secondary air valves shut. That may have been what you were alluding too, just wanted to make sure the poster understands how the secondaries are tied to vacuum.

    You can tweak the secondary opening rate by increasing the diameter (very slightly) of the hole in the vacuum break vacuum line fitting. IIRC, based on application, they could come with different sizes stock. Forgive me, it's been awhile since I've dealt with this.

    Airflow keeps the secondaries open, (which is part of the spring tension setting) engine vacuum keeps them shut.
     
  6. Mad-Dog

    Mad-Dog 1/2 ton status

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    you had a lean backfire that harmed nothing in the carb.
    Quadrabogs have a secondary air-valve that meters air flow thru the secondary's according to engine demand even though the throttle plates may be WFO, you can adjust the tension on the secondary air valve to suit the needs of the engine by loosening the set screw and rotating the spring CW or CCW.
     
  7. jrpeebles

    jrpeebles Registered Member

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    Thanks for all the input.
     

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