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Quadrajet Questions

BIGCHEVYTRUCKDRIVER

BIGCHEVYTRUCKDRIVER

1/2 ton status
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I just bought a new q-jet for my 79 chevy K-10 and on the pass side there are 2 choke looking things 1 obviously is the choke and the other is ?? vacuum secondaries, vacuum kickdown, or ?? and more importantly do these 2 units need constant vacuum or not ?? 1 is chrome with a black cap it is to the front of the carb w/a large vacuum port, the other is smaller faces rear with a small vacuum port. Got the truck to run the way I plumbed it but the secondaries were not working at all. Thanks for any input on the matter.
 
First off, secondaries can't be tested with the vehicle sitting. You'd need the hood and air cleaner off and watch them while driving. Perhaps why you think they aren't working.

Choke is the only thing that will hold the secondaries shut. If misadjusted it's possible. Personally, I don't know that a Q-jet with the secondaries locked out can even move one of these trucks lol.

One of the cannisters is a choke pulloff which pulls the choke open a fraction of an inch once the engine starts, the other is a secondary air valve dampener. It keeps the secondary air valve from "fluttering" as engine load changes. You should be able to tell which is which by inspecting the linkage hooked to them.

No telling how GM plumbed the vacuum lines for both of them throughout the years, but both will work fine/need "unported" (manifold) vacuum to operate correctly.
 
I don't have them here , but I remember most of the secondary lockout vacuum cans get vacuum right off a nipple on base of carb . Most at the rear , short piece of tubing .

The black cap thingy does not get vacuum . That is hot air choke , and predates the electric choke . It hooks up to the heat stove tubes coming out the intake next to passenger side of carb . Usually with a prebent metal line , and short piece of rubber .

You can remove that black piece for a black piece from electric choke carb , and have instant electric choke with a 12 volt switched wire added through a second oil pressure switch added above oil filter ( theres a gallery port there ) :)
 
I suspect he's talking about the vacuum cans, even though he says choke things...really depends on whether this is the "right" q-jet for the truck or not...could be Cadillac, Olds, Chev, you name it, style of choke, but the vacuum cans are pretty universal in design/style, while there was never more than one choke on the carb. :)

I figure we are talking about parts 55 and 320 (or similar) here:
http://dyeager535.topcities.com/CCCqjetdiagram.html

I do recall seeing black caps on some of the vacuum breaks though, unsure what that's for, perhaps different methods of running things, or tuning, etc.
 
Yeah definitely got the right one for 79 Chevy checked the P/N against the required P/n. Had a carb off of a 70 cadillac and a piece of crap at that. Therefore wouldn't pass smog. I will hook both to unported vacuum and see what happens. Also when I had the other carb on there could definitely tell the difference when the secondaries opened up. Secondaries definitely not opening up with the new carb. Thanks for the input.
 
Check that the secondary air valve (upper "doors") opens with your finger (vehicle off of course) then check hot to make sure the choke is fully open and not keeping the secondary throttle shaft shut.

There is a dogleg piece from the choke that can hold the secondary throttle shaft closed if the choke isn't adjusted right. Should be engaged with the engine COLD.

My friend bought a brand new Edelbrock Q-jet, and had all sorts of problems with the choke, out of the box. But that was only because he (nor I at the time) understood the interaction and operation of the choke. I would suspect most problems with the Q-jet from rebuilds or new are choke related.
 
Dyeager Part # 340 on the diagram has a vacuum port on it should it have constant or not
Part # 320 also has a vacuum port on it constant or not

When I disconnect the constant vacuum line off of Part # 320 the secondaries work fine what do you think ?

Thanks for input
 
The stove pipe off of the intake pauly383 talks about would that go into the opening on the passengers side of the intake where there are 2 threaded holes and the hole itself is square if so what is the piece that goes from the square hole to the "stovepipe" and can I buy it at any parts store.
 
Pauly is right then, that's the choke you are talking about...I'm guessing thats supposed to be hooked up to the hole on your intake.

Haven't dealt with the Chev style of the hot air, but sounds like he has. :)
 
Well I found the problem when I switched carburators I went from a remote choke to a integral choke so now I need to know what to call the plate to switch from remote choke to integral choke. So a parts guy can understand me and get me what I need.
 
You will be switching to an electric choke then I suppose, if it will bolt up to your carb body. Apparently rare that they won't, but some will not.

Diagram I linked to shows the electric choke components, you will be best off getting them from a wrecking yard. The electronic portion of the choke (the bakelite cover with circuitry) was pretty expensive for what it is, last I checked.
 
I actually dont know if I can upgrade due to stupid Cali emissions. So I am going to try to run the required choke tube as I have found it called. Heading to Hust Bros today to try and get the right one for the application.
 
Ahh yes. Good luck with Cali emissions.

Really stupid that something that has no bearing on emissions (when adjusted correctly) has to be worried about.
 
My next question Is if any one knows is the hose from the intake manifold to the choke mechanism open all the way through? What I am thinking of doing is drilling and tapping the old remote choke plate, attaching a metal tube to it and then attaching the rubber hose to it and the choke mechanism.
 
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