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Mecahnical secondary Quadrajet, I have one, why not hear about this?

Discussion in 'The Garage' started by sled_dog, May 4, 2003.

  1. sled_dog

    sled_dog 1 ton status

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    I just went over to a family friends house. He converted my stock 84 Quadrajet to a Mechanical secondary. Pretty much just remove the vaccum crap and tune the air screws. Shes got more power for certain, why don't I hear about this here? I have never heard of anyone here doing it. My secondaries before weren't even opening thanks to a fudged up linkage. She hauls in fourth gear now and it never did that before. I still need lower gears and maybe tune them to open a little sooner but its nice so far.
     
  2. Suburbanite

    Suburbanite Registered Member

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    Don't know much about carbs but wouldn't switching to mechanical 'fix' the tuning to a particular rpm range. For example, good at high rpms but bad at low rpms (or vice versa).

    Also, I thought the QJ wasn't much liked by most people. I think it had/has to do with difficulty tuning it but I've read once it is tuned properly it can produce as good or better fuel mileage than a TBI equipped vehicle. But, again, (I think) that's within a relatively narrow rpm range.
     
  3. sled_dog

    sled_dog 1 ton status

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    yeah he was saying you have to tune it to come on when you want. And so far I am not sure. It doesn't seem to come on soon enough in second and third but fourth its perfect. Which doesn't make too much sense to me. Cause why woudl it come on at lower Rs in fourth as compared to the others? I am going to cut up my air box see if giving it more air makes a difference.
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    So theres actually now a rod added to the secondary air valve that opens them? (the large butterflies at the rear of the carb) Fuel metering is done with the secondary air valve movement, if this is still controlled by airflow, as they are stock, you have a vacuum secondary carb, still.

    Without a rod to open them, the carb is still "vacuum secondary" even though the air valve is held shut only by the spring.

    You probably don't hear about it much here because there isn't much point to it, except maybe racing.

    If they weren't opening before, saying it has more power really doesn't mean much, except that its now operating close to the way it should have been in the first place.
     
  5. sled_dog

    sled_dog 1 ton status

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    that was kind of what I menat when I tacked on the fact they never opened. And yes it realy is still vaccum opened just without all the vaccum crap on the side of the carb.
     
  6. blueturd

    blueturd Registered Member

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    Very curious if you could get some pics up. I use a qjet on my H/SA camaro (drag car), always looking for 5 hp! /forums/images/graemlins/rotfl.gif
     
  7. florida4x4

    florida4x4 1/2 ton status

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    I understood the best thing about the qjet is that when it's setup properly it gives the engine exactly what it needs and no more/less. making it a mechanical secondary is patching other problems. Oh yeah, and it voids the warranty /forums/images/graemlins/rotfl.gif
     
  8. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    [ QUOTE ]
    that was kind of what I menat when I tacked on the fact they never opened. And yes it realy is still vaccum opened just without all the vaccum crap on the side of the carb.

    [/ QUOTE ]
    All he did was take out the choke lock out. If the choke had been properly set up then it would have done the same thing. THe other thing that he did by taking the vacuum pot of is that Vacuum pot slams the doors shut when you get off the throttle. Early quads didn't have this at all.
    Other then bypassing the orginal choke problem (that it doesn't sound like he addressed at all) I don't see a single gain to what he did.
     
  9. Steve D.

    Steve D. Newbie

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    You are %110 correct sir and the heat coil on the side opens the choke which interns unlocks the secondaries. All I ever needed to do is bend the half inch metal bar that stops it from locking the secondaries out, and you could always bend it back if needed, but if it was cold the engine would bog down. The engine has to be HOT before you can dump copious amounts of raw fuel into the engine!!
     
  10. diesel4me

    diesel4me 1 ton status Premium Member

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    You do realize the thread is over 13 years old,right ?...:)
     
    blazer74 and ashman like this.

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