Quadrajet Secondaries ? - Team Camaro Tech
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post #1 of 8 (permalink) Old Mar 22nd, 03, 04:46 PM Thread Starter
 
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How do the secondaries on a qjet open. At WOT they are suppose to open by load. Right? What part of the carburator actually opens it? I ask this because my carb does not seem to have a vacuum canister to open the secondaries. It only has a canister to open the primaries.

SoFast
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post #2 of 8 (permalink) Old Mar 22nd, 03, 04:55 PM
 
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They suck open under load and rpm's!!

And there is a real little allen wrench setscrew under or in back of the pass. side end of the secondary air valves shaft that can be loosened and then using a small straight screwdriver in the pass. side end of the shaft, you can adjust it's opening and closing set.

BUT be forewarned that you may kick off the little bitty tension spring and have to start from zero if you lose the original setting...

I always played with mine like at about an 1/8th to a 1/4 turn with the screwdriver either way to get the sucker set where I liked it...

Anybody else got anything more to offer here??? pdq67



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post #3 of 8 (permalink) Old Mar 22nd, 03, 05:06 PM
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Al
 
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It's been a long time since I looked at or worked on a Q-jet, so I'm going from memory here. If I'm wrong, I'm sure someone will jump in and correct me...please do!

As I recall, the secondary throttle blades on a Q-jet are opened mechanically, and they can only be opened when the choke is fully opened. There is a metal plate that covers the secondary venturis, and these are somehow vacuum operated(I'm sure it's way more complicated than that), and open progressively as the engine requires more fuel/air. This plate is connected to the secondary metering rods..as the plate opens, the rods are pulled upward and more fuel is added.

Like most carburetors, it operates on the same basic principle as your toilet, with a few extras thrown in.

I think the vac cannister you see on the primary side is a choke pull-off...it keeps the choke valve from completely shutting off air to the primary side. Also called a vacuum brake.


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post #4 of 8 (permalink) Old Mar 22nd, 03, 05:10 PM Thread Starter
 
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I think I am just confused and wanted to know if the vacuum valve canisters have any thing to do with opening up the secondaries.

SoFast
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post #5 of 8 (permalink) Old Mar 22nd, 03, 05:22 PM
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Quote:
Originally posted by SoFast:
I think I am just confused and wanted to know if the vacuum valve canisters have any thing to do with opening up the secondaries.
I believe you are talking about the choke pull-off(s)

Edit: BPOS I just saw your post

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post #6 of 8 (permalink) Old Mar 22nd, 03, 06:56 PM
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pdq and bpos are both right. The seconary butterflies are opened mechanically. The secondary top plates are opened by vacuum since the shaft if off-center of the "air valve". The air valve also lifts the secondary metering rods.

Any "vacuum valve canistors" you're seeing are probably choke pull-off and choke pull-off dashpot. The dashpot is a confusing device when you look how it is connected. Basically, it helps hold the choke open between cranks to prevent choke flooding. There is no vacuum actuator like on holley's. Just the offset air valves above the secondary venturies.

-dnult

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post #7 of 8 (permalink) Old Mar 22nd, 03, 08:26 PM
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The choke pull-off also doubles as a device to hold the secondary air valve shut while the engine vacuum is high. You can adjust the rate of release of this dashpot to help control the opening of the air valve.
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post #8 of 8 (permalink) Old Mar 26th, 03, 09:20 AM Thread Starter
 
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Confusion cleared.

Thanks

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