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Carburetors Carb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.

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Old 03-25-2007, 11:19 PM   #1
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Mechanical secondaries VS vacuum secondaries?

What do you prefer? I am experiencing a major bog in my TA right before my quadrajets vacuum sec's open and I am thinking about getting a 4brl with mechanical sec's rather than rebuild the quadrajet. However I have never owned a carb with mechanical secondaries and I was just wondering if they are any better or I should say do they have a smoother transition between 2brl operation and 4brl wide open throttle. The TA is so bad right now when I floor it, it nose dives for about a full second and then takes off like a bat out of hell. The motor is a 350 with a mild cam and 202 heads probably putting out about 300hp so I was thinking maybe a holly 650 with mech sec's as this is more of a red light to red light and in town cruiser and will hardly ever see anything above 5500rpm. Looking for any and all suggestions.
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Old 03-25-2007, 11:24 PM   #2
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Re: Mechanical secondaries VS vacuum secondaries?

Quadrajets don't have vacuum secondaries. Have you tried adjusting the secondary air valve tension?
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Old 03-26-2007, 10:40 AM   #3
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Quote:
Originally Posted by 4playta View Post
I am experiencing a major bog in my TA right before my quadrajets vacuum sec's open ...
Actually, you are experiencing a mojor bog when your quadrajet secondary air valve (AV) opens too quickly, which lasts until the air flow can finally draw fuel through the secondary fuel metering passages and feed the air that is already flowing through the too-open secondaries.

You need to adjust the secondary AV tension, which is discussed in the tech article about getting the most out of your q-jet, linked from the home page. You may also have a bad or disconnected choke pull-off, which plays a part in this, too. The way this is supposed to work is the pull-off and tension keep the AV closed when the throttle blades first open, then slowly open the AV so only a little air flow is allowed into the secondaries, enough to start pulling the fuel in, and then the AV opens to full flow. It's mainly a trial-&-error adjustment - add tension, test drive; readjust, test drive, etc., until you don't feel the secondaries open - If you can feel them open, you are bogging and you need to add a little more tension.
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Old 03-26-2007, 11:41 PM   #4
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Re: Mechanical secondaries VS vacuum secondaries?

Thanks I tried this today and it took me about 2 hours to get it just right but boy what a difference...very snappy acceleration and I got it so the AV for the secondaries opens at about 3700rpm and it opens smooth with no bog.

And I was going to buy a new carb...like I said thank you again!

Everyone I ever talked to says quadrajets are junk but my car is running ripe...gonna go out and kill me a civic with a cold air intake and a wing this weekend, LOL!

Last edited by 4playta; 03-26-2007 at 11:45 PM.
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Old 03-31-2007, 10:13 AM   #5
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Re: Mechanical secondaries VS vacuum secondaries?

but a holley and be done with it,,, you have no secondary accel pump...

650 dbl pump will solve all your problems
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Old 04-02-2007, 03:50 PM   #6
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Re: Mechanical secondaries VS vacuum secondaries?

no need for a holley on these cars. the qjet is not the limiting factor. sure if you want one buy one , and the adaptor to make it fit on your manifold too. but its not nessicery
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Old 04-05-2007, 01:06 AM   #7
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Re: Mechanical secondaries VS vacuum secondaries?

No need for a double pumper in one of these tanks anyways...
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Old 04-05-2007, 12:15 PM   #8
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Re: Mechanical secondaries VS vacuum secondaries?

get the holley dp and dont look back.
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Old 04-05-2007, 12:15 PM
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