Secondary actuation lever on primary shaft

[Cadman-iac]

  First off, great website, wish I had found it years ago. I'm new to the site but not to Quadrajets.

  Over the years I've noticed that the Quadrajet has used 3 different length levers on the primary shaft that the linkage going to the secondaries connects to.
 The purpose is to change the point at which the secondaries begin to open.
 The shortest one is the most common from what I've been able to see. It allows the primaries to open appropriately 50-55% before the secondaries begin to operate.
 The longest one allows the primaries to open approximately 70-75% before you start to use the secondaries.
 (These are just guesses on the percentage as I don't have a gauge to measure the actual opening).

 But my question is what exactly was the reason for having the secondaries opening later? I do know that it causes them to open much quicker once they do begin to operate, as you don't have as much primary travel left before you hit the maximum opening.
 
 I have 3 different books specifically on the Q-Jet and this is not mentioned in any of them.
  I noticed this when I began to disassemble my collection of Quadrajets for parts to tune with. Unfortunately I only realized it about halfway through, but once I did I recorded the numbers on the long lever ones. The two I have numbers for before I took them apart are the 17057512 for a 77 454 and a 17085226 for an 85 305/350. I have about 7 primary shafts that have the long levers on them, and 1 with the medium length lever, and all the rest are the short lever.

 I was just wondering if anyone else has noticed this, and if you can explain the advantages to one over the others.

 What I've concluded is that the long lever allows you to use the primaries more before tapping into the secondaries, giving you better fuel economy. I don't know if this gives you any performance increases.

 Thanks, Rick

 P.S. I'll post pictures when I figure out how on this site.

[Cadman-iac]

 Ok, here's a picture of the 3 different levers used on the primary throttle shaft that activates the secondaries.

 I removed these from the shafts in order to get accurate measurements on them, as trying to do it while they're on the shaft is difficult at best.

 Also, to identify which one you have if you want to know, the easiest way is with the carburetor throttle plate assembled.
 If you're looking at the carb from the "driver’s" side, the linkage between the two shafts will tell you. The shortest lever has the linkage going downhill, meaning that the secondary end is higher than the primary end.
 The longest lever has the linkage between the shafts going uphill, the secondary end is lower than the primary end.
 The 3rd, medium lever keeps the linkage level between the shafts.

 Initially I thought that the long lever was used on large displacement engines, like the 454 and Cadillacs 472/500, however after looking up the number for the second carb I recorded, it's used on 305's and 350's, so that theory goes out the tailpipes.

 Cliff's book makes no mention of this either.  Maybe he can shed some light on this for me though, I'm sure he's noticed it.

 Rick

[Pav8427]

Never noticed this before. I too would be interested in reasons why they did this and how it may apply to possible set up for certain applications.
Would guess these are a swappable part if one so desired.

[Cadman-iac]

  They are swappable, if you swap the whole shaft, or you can remove the linkage bracket by grinding the end off of the shaft and removing it to get to the actuation lever. It rides on a sleeve that is used to space the accelerator pump bracket and the linkage bracket if memory serves. I'm not in my shop at the moment so can't eyeball one to be sure.
 But if you do it this way, you will have to either weld your bracket back on, or peen the end of the shaft if there's enough material left after you have filed or ground it to get the bracket off. I've done it both ways, the best being peening as it looks like the original method.

 Yes, I'd love to know if changing the actuation point and rate of opening has any advantages.
 The long lever allows more primary usage before the secondaries kick in, but once they do they open much quicker.
 The only thing I can think of is it may make it easier to get better fuel mileage because you're not getting into the secondaries as much.  You can keep your other shoe on, lol!!

 Rick

[Cadman-iac]

 Here's some more pictures showing what I was referring to. The first one is with the long lever, the second is the short lever.

  This 3rd picture is of a primary shaft showing the order of the various pieces on it. What looks like a spacer also acts as the pivot point for the secondary lever.

 The 4th picture shows a short and a medium lever and the pivot/spacer off of the shaft.

 The 5th one shows a couple of different spacers. The one that is rusty came off of a Dual Jet, you can see it's even from side to side, unlike the other with a step for the lever to ride on.
 Something else to watch out for if you're going to be building your own primary shaft from various parts is there are several widths for the spacers depending on the model of  carburetor. The early ones had a narrower throttle plate assembly and the shafts were shorter, requiring a narrower spacer.
 But the Cadillac carbs used a slightly wider base/ throttle plate, but not as wide as the following models used, so double check the shaft lengths before you start changing the parts around.
 I wouldn't recommend doing this except in a special case where you simply can't find a usable shaft with the right bracket for the linkage, because the shafts don't have much extra material once you file down the end to remove the bracket.   If you're lucky you may have enough left to peen it over the new bracket, otherwise you will have to weld it in place, and if you don't have the pieces together in the correct sequence you'll be starting over on another shaft.
 This has been my experience with these, and I thought I'd share it with the site in hopes it will help if you find yourself in need of a custom shaft for your carburetor/application.

 Rick