Warning, this is a really long thread, because I have an annoying tendency to be excessively verbose. To make a long story short: A standard trans is not an automatic trans, your carburetor CAN tell the difference, and don't listen to the automatic guys when they tell you how to tune your secondaries, because they won't be right. Now, begin long, excessively verbose, post: ------------------------------------------------------- Ever since the first time I bolted a Quadrajet to my car, I've had various problems with the secondaries. I've had the same problems with more than three different Quadrajets on the same vehicle (two computer controlled, one not). No matter what I did, I could never get them dialed in right. Either they opened too quickly and bogged, opened too slowly causing the car to be slow when floored any time about 2000rpm, or they'd exhibit a bizarre behavior that's been my personal bane for a couple of months now that I've never heard ANYONE else complain about. When floored from a dead stop, the car performs excellent. When floored from cruise, the car bogs and then quickly recovers and proceeds to get up and boogie. However, I noticed that the first time I actually raced the car, it would "lay down" very badly on the 1st-2nd shift. The higher I ran the engine in 1st and the faster I shifted, the worse it would get. Sometimes I could hold the gas down and it would eventually recover, other times it would basically stop accelerating, requiring me to completely get out of the gas before getting back into it. I originally thought it was the secondaries not opening, but a few people who were watching my car noticed that everytime it did this, it would blow clouds of black smoke out the tailpipe. This problem was worse the looser the air valve spring tension was, but even resetting it to the "stock" setting did not completely cure it. It removed the problem when driving normally, but at the track, I found that it would still lay down occasionaly if I shifted very fast. Tightening the air valve spring much tighter than stock eventually got rid of the problem and exchanged it for another one, causing the secondaries to open too slowly when punched from a roll (it did, however, eliminate the problem from a standing start). Keep in mind the entire time the car was using the stock vacuum canister, which I believe opened in 2.5-3.0 seconds. I talked to several people trying to figure out what I was doing wrong, but not one could figure out how to fix it. Everyone insisted they never had seen or had a problem like that, and none of them had done anything more than run a loose tension on the air valve and the stock vacuum can. I believe Ed M even told me he basically ran NO tension on his old car and never had a problem. For the hell of it, I removed the vacuum can and plugged the port, and turned the spring tension way up. It was a night and day difference, however I was unable to get enough spring tension to completely eliminate the initial bog (as at least one person on this board will tell you). This is probably the point where you say, "You, my friend, should put down your wrenches and go back to some nice safe hobby, like playing Quake over the internet," and where I say, "Ah, but wait, there's more!" At this point I was getting rather pissed off and thinking that maybe converting to TBI was a good bet so I could have a legitimate excuse for having such a slow car. I returned the vacuum can to its proper place and reset the air valve tension to something slightly looser than stock (about .5 turns, IIRC). The next time I was at the track, I decided to try something different. Since the car insisted on laying down when I got back on the gas after a shift, I figured well then, why not try never getting out of the gas at all? And hot damn if that didn't work like a dream! Power shifting the car allowed it to haul even through the shifts, and it NEVER hung up or did anything stupid, even after loosening the A/V tension to nearly nothing. It was then it hit me--everyone I knew running the stock vacuum can and loose A/V tension was running an automatic transmission! And everything suddenly started to make a WHOLE lot of sense. What was happening when I was racing the car while shifting normally is that I was outshifting the secondary air valve. Getting back in to the gas (and opening the secondary throttle plates all the way) before the airvalve had a chance to close was causing ALL sorts of problems. That's why the problem got better as I applied more spring tension--it allowed the air valve to close completely during the shift. Keep in mind the stock vacuum break actually does you little good here if you're a quick shifter--a vacuum break that's slow to release is also slow to pull in. In fact, by timing the vacuum break on the car and comparing it to my shift speed, the break didn't even get enough time to retract half way before I was already getting back into the gas. I'm sure you're thinking at this point, "Hawk, my friend, you are smoking crack. That doesn't make any sense--why doesn't that affect my automatic?" Well, because with an auto, you NEVER get out of the gas and get back into it again that quickly. Think about it. The air valve and the throttle blades stay open all the way the entire way down the track. And I'd bet you dont' make a habit on the street of flooring the car, letting up, and flooring it again within the space of a second. Generally in an auto, when you do let up on the gas, you're EXTREMELY unlikely to floor it again before the vacuum break is able to take its two seconds to close the air valve up again. In fact, with a slow enough vacuum can, I'd bet you could get away with no air valve spring tension at all. It turns out that the hot setup for a Quadrajet's secondaries on a manual transmission car is completely the opposite of what you want on an automatic. On an automatic, you want weak spring tension and a slow to moderately slow vacuum can. On a stick shift, it seems you want a fast vacuum can and a lot of spring tension--at least if you know how to shift. I now have a 1 second can on my car and the stock 7/8 turn on the A/V spring. The car EVER SO SLIGHTLY lays down after the shift and bogs noticeably when floored from a roll. By the time I have the spring tension tight enough to get rid of the bog, I'm confident the secondaries will close fast enough after a shift to prevent the problem. If you have a stick and can't get rid of the dreaded bog or are having problems like I did, give it a shot. If you have an automatic, ignore everything above this point and stop telling stick shift guys to use slow cans and loose spring tension. And if you have a stick shift and a slow can and loose spring tension and it works great, either A) you don't shift it fast enough, or B) my car is a total aberration and wants to be tuned completely different than every other Quadrajet in the planet. And if it does turn out to be reason B, don't tell me. I don't want to know. If you want to complain about reading my excessively verbose post, first go back and read the top of the post, and then take $0.35 and call someone who cares.

Just get a double pumper already

Even a holley vacuum secondary 'comes in' much nicer than a q-jet. In my experience with q-jets, automatic or stick, I remove the vacuum can and adjust the spring tension.

Thats the draw back of the Q jet secondaries being so large. Even tho the boosters are pretty sensitive, they still can't open/close as fast as a squarebore VS without bogging.

Even my automatic seemed to like a fast can with moderate spring tension. I don't recall anyone advocating the slow can, although I could be wrong.

BTW... where did you get the one second can? Last time I needed one, I got lucky and found a used one in a pile of spare parts. Do you have a part numer for a new one? Thanks.

I got lucky with the one second can. It came on one of the junk carbs I bought on Ebay.

I think a street car needs a fast can for all applications. Check out this scenario:

You are merging onto the freeway from a 30 mph roll. You stab the throttle, and the automatic transmission downshifts to first gear, and the rpms instantly climb to ~4000 rpm. You can use the secondaries under this speed and load condition, but by the time the slow can releases the air valve, you are already out of first gear.

I don’t buy the “slow can for automatic cars” theory.

I guess I violated my own rule...

Don't listen to me when it comes to tuning the secondaries on your Automatic

A lot of times when I run MUCH slower cars I'll hold the trans in 2nd or 3rd and hop the car next to them (completely letting off and nailing it rapidly, like manual trans shift) - with no ill effect on the secondaries once WOT again. That's on the stock can with the hole drilled out and AV at 1/4 turn past zero tension.

But then again my QJet runs great! Much better than the few others I've driven. I may be a bad example?

99hawk, can you describe what you did to someone who doesnt know as much as someone like yourself about the tension springs? I bought a rebuilt cc-qjet a few months ago and i hear people talking about bogging, but what the hell is bogging? That hesitation that it makes when i floor it? How do i ajdust the spring, and where can i get one of those one second cans, and what the hell do they look like???

i had the same EXACT problem your having hawk. No matter what i did i couldn't get rid of the bog. I always sorta knew that a quicker can would do wonders for me, but i didn't even know they existed, let alone where to get one. So i solved my problem by getting a Demon 750DP Haven't had a bog since....

Eric

Why are you drag racing by letting off the gas and then flooring it again with an automatic? I just put it to the floor and it hits about 3800 rpms and shifts again without letting off the gas. A lot of times I love racing guys that let off the gas and then upshift to the next gear with an automatic. Why do they do that?

Who are you asking?

I have no idea. I have a stick shift so I doubt he's talking to me.

Anyhow, whoever asked, the 1 sec cans are hard to come by. I bought a bunch junked Qjets for parts and got lucky.

If you're in and out of the gas a lot there's something you should try other than a slow can. On some cars I have found this works real well.

There's a little roll pin that acts as the fulcrum for the secondary rod hanger. Shove a piece of wire through it and it will hold the secondary air valves partially open at all times. Make sure the wire won't come out and make sure you readjust the linkage on the vacuum break so it's not applying force to try to close it beyond that point.

Kinda similar to what you're doing, but there are differences. Too much to write. Try it and see if it works.

Use a fast can and some moderate tension on the spring as a starting point.

Try to do your own modifications to the
vacuum cans instead of trying to find them in junkyards. Just cut the tube at the elbow and increase the tiny hole by
inserting a regular pin (from a new shirt).
This will give you a fast can, about 3/4 to
1 sec is what you want. Secure the tube
back on with JB epoxy. I run this can with moderate spring tension and my car
has never had a bog. In fact when the secondaries open the car jumps!

"If you can feel the secondaries opening, they're opening too soon."

In other words, it's bogging.

It's hard to believe, but he's right. You should never feel the car jerk when the secondaries open. It should be a smooth increase in power all through the power band.

Try tightening the spring a little more.

Sometimes with the QJet you can feel the secondaries open becuase they open so SLOWLY that the motor is being held back. When they do finally open there is a significan rush of power- one you can really feel.

When you bog the QJet's secondaries you'll know it- it'll fall on it's nose for a plit second, then recover and take off likea bat outta..... you know.

An interesting read.

I've experienced several of these symptoms with my QJet. But now it comes on in a steady fashion, yet the secondary action is very noticeable without any bog. I think that's how QJets run when tuned properly.