QJet Secondaries

davesdeville · #1 (**permalink**) 10-08-03, 06:24 PM

I was going to fool around with my carb today and see what I could see. I can't see the carb when I'm in the car pushing the gas, so I got my dad to look at the secondaries and see if they're opening. When I floor it, the secondaries won't open. I tried in neutral and then again with the brakes locked in drive, which as I expected made no differance.

What's up with that? I mean what can I do about it? Any linkages I should check, vacuum lines, anything?

davesdeville · #2 (**permalink**) 10-08-03, 08:19 PM

I found a vacuum tube that had a screw on the end of it (to seal it) connected to the carb. I found a place where it looked like it was missing a vacuum tube, and I put the tube on it. I stood back for fear of something weird happening, and floored it, low and behold the secondaries opened slightly. So now I think I need to deal with the accelerator pump and I'll probably rebuild it. Then I hope I'll be good to go.

MMNineInchNails · #3 (**permalink**) 10-09-03, 01:02 AM

See, this is why we need a classic caddy section so someone can givehim a quick reply that knows about Q-jets.

Also look where your choke is linked up at. On my carb, a little piece from where the choke linkage connected up was in the way from the secondaries completely opening. Probably not the case with yours, but just making sure.

davesdeville · #4 (**permalink**) 10-09-03, 01:48 AM

I looked at it again, and tested it again, and they still weren't opening up. It also looked really dirty throughout the whole carb, plus the gasket between it and the manifold looked like it had a crack. So I took the carb out, I plan on a full cleaning and rebuild for it.

Katshot · #5 (**permalink**) 10-09-03, 06:54 AM

The vacuum line you connected was probably to the choke pull-off on the right side of the carb. If you don't activate it, the secondaries are "locked-out" basically. The other thing that will keep them "locked-out" is the choke itself. If the choke is even slightly closed, it will keep the lock-out pawl (a little foot-shaped link) engaged with the secondary throttle shaft pin (a small pin that goes through the secondary throttle shaft on the right side of the carb). Once the choke is COMPLETELY off, then the secondaries will open. Your carb MAY also have another vacuum pot on the right side of the carb connected to the secondary linkage. This is to prevent the secondaries from opening too quickly. It controls how fast the upper butterflies open. This will help control the "bog" that is often present in these applications.

blue_eldo · #6 (**permalink**) 10-15-03, 03:38 PM

Quote:

Originally Posted by davesdeville

I was going to fool around with my carb today and see what I could see. I can't see the carb when I'm in the car pushing the gas, so I got my dad to look at the secondaries and see if they're opening. When I floor it, the secondaries won't open. I tried in neutral and then again with the brakes locked in drive, which as I expected made no differance.

What's up with that? I mean what can I do about it? Any linkages I should check, vacuum lines, anything?

There is a thermo lockout device that will not allow the secondaries to open unless the engine is warmed up!
The Qjet is a very complicated device. it is easily screwed up, but when working correctly is a beautiful thing.
I have two of them, on a 72 Eldorado and another on a cad500 powered GMC motorhome, and it took me awhile to get them dialed in.
Get the Doug Roe book on Qjets.

brougham · #7 (**permalink**) 10-15-03, 06:05 PM

The thing I like best about Quadrajets is the electric choke. No more problems because the heat passage is full of carbon

But I went with another carb since my QJ needed a rebuild and this wasn't on a Cadillac anyway so it probably has no relevance here

davesdeville · #8 (**permalink**) 10-15-03, 08:10 PM

Well I got finished rebuilding and re-installing the QJet yesterday.. Except a screw that holds the metal piece that the chokes metal spiral pushes against fell down a hole where I can't get it back... But it seems to work a lot better, and I'm still figuring out how well it's working and if I need to do any adjusting.

Night Wolf · #9 (**permalink**) 10-15-03, 10:06 PM

one thing I read somewhere...the secondaries on the Qjet do not open all the way, only 60-80& there are metal "tabs" that prevent this, and if you file the tabs down, you can get them to open 100%, then squeeze a little more life outta the 307....

....although I read somwehere the biggest thing with the 307 is the size of the ports on the heads and that is is sipping through a straw, I wonder if that is true or not and if someone got beter free flowing heads, how much better that would be.

Katshot · #10 (**permalink**) 10-15-03, 10:22 PM

The Q-Jet opens PLENTY far for a 307. You CAN change the jets a little if you want though.

Shoehorn · #11 (**permalink**) 10-22-03, 12:54 AM

Quote:

Originally Posted by davesdeville

I found a vacuum tube that had a screw on the end of it (to seal it) connected to the carb. I found a place where it looked like it was missing a vacuum tube, and I put the tube on it. I stood back for fear of something weird happening, and floored it, low and behold the secondaries opened slightly. So now I think I need to deal with the accelerator pump and I'll probably rebuild it. Then I hope I'll be good to go.

It's very possible that a former owner of the car killed the secondaries deliberately to save gas, and avoid the embarasing backfire the quadrajunk likes to do about 10 seconds after you shut the engine off.

The Q-jet on my 80 Coupe DeVille was so bad that I could make it backfire anytime I wanted to. All I had to do was put it to the floor for a second or so, and jump off the gas. 1-2-3... BOOOM! Flame could be seen in both side mirrors. Was my interstate revenge system for people who liked to ride my ass. Belch flame on them one time, and they back off.. worked every time.

Unfortunately, I wreaked that car at about 75mph, glancing off concreet walls. The impact that ended the ordeal was suffieient to throw me into the steering column and break it off. I probably could have avoided that accident if i hadn't lowered it and put 195/50/15 tires on it. I wasn't hurt, btw. I still went to work that day.

DaveSmed · #12 (**permalink**) 10-22-03, 01:47 PM

Quote:

Originally Posted by Shoehorn

It's very possible that a former owner of the car killed the secondaries deliberately to save gas, and avoid the embarasing backfire the quadrajunk likes to do about 10 seconds after you shut the engine off.

I've had that one happen. Fun stuff, especially if it happens right after you get a custom dual exhaust system put on a week before, and blow the muffler up from the backfire. Fixed the backfire problem, but still didn't fix the muffler.

davesdeville · #13 (**permalink**) 10-22-03, 08:06 PM

I never had one backfire on my 75 or 78. So maybe I'm lucky..

Katshot · #14 (**permalink**) 10-22-03, 09:54 PM

If you have a back-fire issue, it's because you don't have it adjusted correctly. I've NEVER had a back-fire issue on ANY Q-Jet I've had and that numbers in the HUNDREDS!

DaveSmed · #15 (**permalink**) 10-22-03, 09:56 PM

Yup, they guy said it started happening right after he took it to get the carbuerator "tuned". I fixed it and it's been fine ever since.