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Secondary Tuning

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blazer_Boy, Jun 18, 2002.

  1. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    What is zero tension on the spring controlling the secondaries on the Q-jet. Say you loosen it up so the air valve flops open then slowly tighten the screw until the air valves come to a close. Is that point zero tension? Or if you slowly let off on the screw driver it will come back a little from spring tension. Basically is 0 when the valves closed with the screwdriver in, or valves closed and no screwdriver holding the screw.
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Zero tension IMO would be as if there was no spring there. Obviously thats not what you want, I'd shoot for *just* closed (but every time, not just some of the time, and when released slowly, not left to "slam" shut from full open) by spring tension alone, then shoot for "perfection" from there.
     
  3. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    I know its kind of a silly question because the real indicator should be how it responds. Am I looking for good repsonse of the line or floor boarding it when cruising. I got the doug roe book and finally got good primary repsonse. Thats why I was going ape defending the edelbrock carb. I had 71 jets with 53 rods and it was flat and wouldn't wrap real well. The edelbrock setup really brought it around. So the baseline tension would be with the screwdriver still in there? With that way it will come back up, but slowy and will come open easy.
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    IMO you have to look at both off the line and cruise/WOT. Either way, if the secondaries are TOO loose, or over rich, or the hangar operates too fast, you may end up with a stumble as they open...you open them too far or dump too much gas through the secondaries you *can* starve the carb of fuel. I've done it, but with a 415CID motor...leaning out the secondary rods JUST a touch allowed the fuel pump to keep up. (these were constant WOT blasts from idle)

    I'm really not sure whats required to OPEN the secondaries air flow wise...as tight as I've seen some stock Q-jets, I imagine if you REALLY wrap the motor out, it would still open up. But that really requires some serious velocity...

    I don't like the idea of slow closing secondaries...when I let off, I want them to close. You'll end up dumping extra fuel on decel. Again, I check to make sure that in ALL cases they close fully, no matter what position the air valve is in when I let go, or slowly allow them to close.

    I read it in the Roe book, and I tend to agree, that the stock snorkel forces the incoming air to flow over the secondaries correctly, so thats something to contemplate. I kinda doubt cowl induction Q-jet cars were setup that way, but I've never looked at one.
     
  5. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    I was out fiddling with it today and my mom could hear me out in the garden. I was going down the highway at the bottom of the cliff by our house. Which is about 150 feet up and three blocks away /forums/images/icons/smirk.gif . I figured merging on to the highway would be a good place to gun it. I'm still running the DR secondary rods that the carb came. They're a medium tip rod and are supposed a good all around rod. Switching to an E hanger helped a ton though. I was running a K. I'm just glad that the cam pulls tremendous vacuum (like 22" at idle) so the power piston spring can be left alone. I've got access now to that little stop for the power piston I was talking about earlier. I just undo a plug on the air horn and stick the little tool I made to adjust it. As far as I can tell its used to adjust rod height at high vacuum cruise situations so they aren't in too far. Man, if I had more money, I'd buy and air/fuel meter. Or at least do the cheapie setup and use a voltage meter. Thanks for the help /forums/images/icons/wink.gif
     

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