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quadrajet secondaries not working?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by weisel, Jan 23, 2002.

  1. weisel

    weisel 1/2 ton status

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    I have a 77 chevy k5 400 (dont know if this makes a difference on the carb or not), and was haveing some problems with the carb. So I rebuilt it, and now the secondaries are not opening. This really bites driving around with the equivlant of a two barrel. I am having semi's beat me up hills. If I knew how the system worked, then I could be able to attack the problem, but I just dont understand. Any help would be great.

    Insurred by Smith & Wesson
     
  2. BurbinOR

    BurbinOR 3/4 ton status

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  3. BorregoK5

    BorregoK5 1/2 ton status

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    The secondaries are vaccuum actuated so check your vaccumm lines and their location first thing. With the engine off and cold the choke actuates a lever which holds the secondaries closed so be aware that unless you manually open this first then actuating the throttle by hand will not open the secondaries. Its a common problem of this system failing and even when the choke is disengaged, the lever holds the buterfly locked closed. I'd look here first. Mine is on the bottom secondary butterfly rod as an external press in pin through the rod which catches on the choke lever (I have a hot exhaust choke so yours may be at the top of the carb instead. Try these first and see what you find.

    I started with nothing and I still have most of that left! - <a target="_blank" href=http://www.echobit.com:81/k5/> Pictures</a>
     
  4. BigBadCad

    BigBadCad 1/2 ton status

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    You might want to check and see if the little plastic cam that actuates the secondaries hasn't slipped out of place or become brittle and broken with age. It's not a part that usually breaks, but it did the last time I rebuild my quadrajet when the secondaries weren't working. It's a cheap part but you'll have to find a shop that carries little odds and ends peices.

    1980 chevy 4x4 1-ton crewcab, 500 caddy, York OBA...work in progress.
     
  5. weisel

    weisel 1/2 ton status

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    I've played with other q-jet equipped engines and as far as I can tell, if the engine is warm and then the throte is opened, the secondaries will start to open, and if your driving and stomp the accelarator, you can hear the engine run differently (the deep throated "wwwhhhaaaaaaap") when the secondaries start to open. Mine dose neither of these things, so I am pritty sure that is not working properly.

    My choke is the type in the intake manifold, so will it be different than your setup? I dont have too many vacume lines running out of the carb, but i've got it hooked up right acording to Hanes or Chilton (I can never remember which one shows vacume routings). One is really short (about an inch long) running to a little diaphram attached to the pass. side of the carb. Is this the one that controles the opening of the secondaries? Or is the vacume drawn threw internaly within the carb and dosn't use a line? Do they open when vacume is applied, or when vacume is taken away? I'll check the choke mechanics and see if there is anything wrong with them when I go home tonight. Thanks for the help already.

    Insurred by Smith & Wesson
     
  6. Burt4x4

    Burt4x4 3/4 ton status

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    I would first check that lock out lever. It is on the passenger side bottom of the carb. The pin on the lower secondary flap is stoped by a finger on the choke assymbly. I was having troubles with mine plus I didn't want anything to block out my secondaries so I completely removed the finger looking piece from the carb. It is there to prevent the secondaries from opening when the motor is cold. I let my rig warm up before driving so I don't need no block out so I removed it[​IMG].

    Another thing is on the top butterfly/flap there is a set screw and tension screw that controls the amount of vacume needed to open the flap, spring tension.
    CAUTION~ Make sure you hold the tension screw BEFORE you turn the set screw or the spring will release ALL of the tension and you have to start all over. Just make minor adjustments, in your case you may need to release some of the tension???
    Good Luck

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
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  7. Triaged

    Triaged 1/2 ton status

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    The secondary air door opens with a drop in vacume (around 5in Hg)

    '71 Blazer CST w/ a 400sbc, 4" lift, 36" Supper Swampers, and alot of rust
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  8. Burbinator

    Burbinator 1/2 ton status

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    If I remember correctly, the short run of "vacuum line to a little diaphram" is the choke pull-off...

    I second checking your choke adjustments/operation as that will disable the secondaries if a malfunction exists.

    Haze gray and underway...<font color=blue>or blue, in my case.</font color=blue>
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  9. Greg72

    Greg72 "Might As Well..." Staff Member Super Moderator

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    My neighbor showed me the levers that actuate the secondaries.....they are closest to the firewall on the passenger side. With the air cleaner OFF you can push on the flaps that cover the seconday ports and FEEL the amount of pressure required to "knock" them open. The stiffer they feel....the more vaccuum it will take to pull them open.

    He described a whole bunch of tweaks that can be done to the acutator assembly to make them open easier....and honestly, I didn't know enough about what he was saying for it all to sink in!!!

    I guess my point is only to check those flaps....if they are sticking, or are HARD to open....you may never get enough vaccuum pressure to pull them flaps open.

    Just a thought from a neophyte Q-Jet owner..... [​IMG]



    -Greg72

    '72 K5 Blazer - 427BB/TH350/NP205/6" Lift/35x12.50's
    <font color=blue>See it here: </font color=blue><a target="_blank" href=http://coloradok5.com/gallery/albun38>http://coloradok5.com/gallery/albun38</a>
     

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