When you first set the choke on a cold motor, the choke slamms all the way shut. The "pull off" is a vacuum solenoid that should open the choke blades 1/8" as soon as the motor starts.

Until the choke is open all the way, a linkage locks out the secondaries. Nothing to do with the pull off, but it is there.

Generally, q-jets bog if the secondaies open too fast. Not opening at all the car would be down on power, but still run pretty well.

Search out a "book" on q-jets, they are on the web. Study up a bit, then watch the carb. Is the choke linkage adjusted properly? Is the choke opening all the way as the motor warms?

The secondaries have both a mechanical progressive throttle plate (low in the carb, connected to the primaries with a linkage) and a spring loaded air valve (you see that one on top.) The air valve is adjustable so it doesn't open too fast. You can hold the choke open and manually work the throttle, you should see the linkage opening the secondary throttle, and lifting the needle hanger which is between the secondary bores at the top of the carb.

 

When you first set the choke on a cold motor, the choke slamms all the way shut. The "pull off" is a vacuum solenoid that should open the choke blades 1/8" as soon as the motor starts.

Search out a "book" on q-jets, they are on the web. Study up a bit, then watch the carb. Is the choke linkage adjusted properly? Is the choke opening all the way as the motor warms?

This has been my first attempt at rebuilding a quadrajet. So far it has proven to be a greater challenge than the Holley’s I re-built in the pass. This is mostly do to all the “coat hanger” rods used for linkage & the “pull off” & such.
My q-jet does what you say it should do when cold. I touch the throttle & it snaps shut. Turn on the engine & the flap above the primaries opens just a bit & the car idles just fine.
The flap above the primaries NEVER comes to like a 90 degree angle though, only maybe like 45 degrees. Could this be my problem when I try to “punch it” a bit?

I have a book on q-jets. After I really got into it, I don’t think the book is well written in some respects. It has very nice detailed color photos & all, but, doesn’t really give “step by step” information on doing a number of things. It doesn’t have any kind of “trouble shooting” information for “tuning” the carb linkage, mixture screws, etc. The book seems pretty helter shelter & incomplete with a bunch of “pretty” color photos. Its useful but could be much better.

 

There is a lot of info here:

http://www.florida4x4.com/tech/quadrajet/index.php

It should help.
The flap above the primaries is the choke and once the engine is warm it should be at 90 degrees. the linkage to it simply need adjustment so that it will open fully.

the secondaries opening usually need adjustment to avoid the bog.
there is an article on adjusting them.

TTFN
Mat

 

Thank you very much! So far, at first glance, this looks like its going to be a very informative site. The first article I clicked on showed & gave great information on "re-bushing" the throttle plate. This is the sort of information my q-jet book touches on. But then the book doesn't go into any "real" details about how to accomplish the task.

 

The secondaries will never open until the choke is all the way verticle, if the lockout link is adjusted right.

Your problem could be as simple as having the "round black cap" turned too far toward "rich."

 

When I was street racing my Chevelles back in the early 70's, I used to love to run Quadrajets, as most guys would think the engine was stock, heheh. You could tweak a Quadrajet to supply all the air and fuel you'd ever need for engines up to 500hp+, which was a lot of power back in the day.

I agree with Jim, your main problem sounds like the secondary lockout is never getting released, due to too-rich setting on choke. Of course, there may be other reason why choke isn't working properly. It depends which choke you have. If you get stuck with a choke problem, post a pic and I'm sure plenty of guys here will have the answer.

-

 

I hate this carburetor!!! It’s the only thing on my car that isn’t numbers matching. Instead of a 7027202 (early type for a 67 Camaro auto) it’s a 7025200, the first year they came out with a q-jet for a 396 engine in 1965. It was a remanufactured carb from long before I bought the car in 2001. It’s ALWAYS had vacuum leak(s). Its gotten worse over the time I’ve owned the car. Anyway, because it’s NOT original I refuse to put too much money into this carb.
I could spray carburetor cleaner all over this q-jet before I rebuilt it. Anywhere I sprayed, the rpm of engine would rev up significantly. I hoped it just needed a new set of gaskets. So I bought a carb kit & replaced the gaskets. No luck. When I put the carb back on the engine, I could spray carb clearer anywhere on it & the engine would rev up. So, I took the thing back apart. This time I smeared a thin coat of RTV on both sides of each gasket before reassembly. I put the carb back on & tested with carb cleaner. The engine revs no matter where I spray the cleaner. It’s like the WHOLE BODY of this q-jet sucks air. I’ve also tested for a vacuum leak by placing my hand over the air horn area. The engine will rev right up. My vacuum gage will jump up to 20 (with my hand over the carb) & hold steady instead of 15 without my hand.
I went ahead & ordered a “new” remanufactured q-jet from Summit specific for my 327/275hp. I’m going to keep an eye out for a “numbers correct” q-jet on ebay that needs to be rebuilt. When I get one, that’s the one I will be willing to put some money into. I’ve read a lot of good things about q-jets, & I like originality.
I just don’t know why this 7025200 seems to vacuum leak all over, not just one or two places. Hopefully when I get my “new” q-jet from Summit the car will run & perform better than it ever has since I bought it. I’m typing all this while half way watching “It’s a Wonder Life.”

 

the only place you should be able to get any sort of vacuum leak is at the base and around the shafts. if it was that leaky all over the carb, there would be gas spewing all over the place. it's also really easy to get spray down the top of the carb when spraying around the carb. smearing RTV on carb gaskets is a waste of time, as gasoline eats it up like nothing.
what kind of gasket are you running under the carb? i've had bad luck trying to get thin gaskets to seal, but the 1/4" thick gaskets seem to last forever and are reusable.

 

Make sure you have the factory stainless steel shim between the intake manifold and carburetor too, or you will be getting exhaust gas going into the intake manifold. Nothing like full time EGR to make your car run crappy.

 

I'm betting those gigantic secondary butterflies are not closing all the way at idle. When I was race-tuning quadrajets, I used to spend a fair amount of time making sure they were well-closed at idle - cleaning and adjusting them as necessary. If you have that throttle plate off the carb, then hold it up to a light source and look for gaps around the secondary butterflies. There is also an adjuster screw, on bottom (underside) of plate, which prevents secondaries from closing too tightly, so that has to be carefully set after you get everything else cleaned and tweaked.

Too bad you're not closer to Rhode Island. I'd say, bring the carb over and we'll play with it.

If it was me, I'd be ripping off that throttle plate and checking the seal of the secondaries.....................

Good luck

 

Does your choke pull of have a vacumn nipple? Does it hold vacumn? If not, that may be one problem. The heat bi metal sets the choke to release when warmed up, but I believe there is also a vacumn pull off too.

 

Does your choke pull of have a vacumn nipple? Does it hold vacumn? If not, that may be one problem.

Yeah I’m going to try that test among others I’ve been reading about at http://www.florida4x4.com/tech/quadrajet/QJet_Tuning_Paper.doc. This guy has some very interesting reading. There are a number of “Tech Tips” for me to experiment with & trouble shoot my quadrajet.
At this point I’m not too worried about the q-jet I presently have anymore. Now that I’ve ordered a new remanufactured unit from Summit, I’m going to use this 7025200 unit for learning. Then when I find a “numbers correct” 7027202, I’ll been much more adapt at rebuilding a quadrajet.

Yeah Novaderrik, I’m using the thick ¼" gasket at the base.
I think the carb I just “rebuilt” has a fair amount of sloop at the base shafts & needs the brass bushings installed. There are a number of other things I should do to this carb to help with vacuum leaks internally. I’ll probably be experimenting with this unit for sometime to come.

 

i personally think that the whole "sloppy shaft bores will cause a bad vacuum leak" deal to be a bit of hype.
i've had some pretty sloppy primary throttle shafts before- like 1/8" wobble- and never had a detectable vacuum leak there. my theory is that the engine vacuum pulls the butterflies down tight against the bore, and the shaft goes down with it, and pretty much seals it off. ever notice that the only time they ever mention it in any of the magazines is when they are at some big name rebuilder that buys a ton of advertising space in the magazine, and they are trying to get you to spend your money there to get that "problem" fixed?