When I was poking around my quadrajet today, I noticed that the secondaries don't open up all the way at WOT. At first I thought it was my throttle cable, but that's not it. If I open up the carb arm (the part directly connected to the primary throttle shaft), when the primaries go to WOT, the secondaries go close, but not quite, wide open (wide open=90 degrees). I can open the secondaries fully (90 degrees) only by turning the secondary linkage directly by hand, but not by turning the primary linkage by hand. So it's not the throttle cable.

It almost seems like the secondary throttle blades are lining up to the baffle under the air horn. Is this the way it's supposed to be? Should I tweak the secondary linkage to get 90 degrees at WOT, or is this a bad idea?
Thanks,
Homer

 

Tweek so that both primaries and secondaries are at 90 degrees when up against the stop.

Sloppy production quality control leads to the conditions you are observing. You are the new QC inspector. Do your duty.

 

hey i have the same problem but dont know a whole lot about the qjet? my secondaries dont open at wot...i think this is part of the reason im bogging real bad and running 17s

 

Homer,
If you want to get 90 degrees you have to do it yourself. GM limited the travel to limit the flow of the carburetor. Most Qjets are 750cfm, far more than a 305 or even a 350 really need unless you're racing 100% of the time. By limiting the travel, the opening is smaller and less air flows.

Fast86,
Bogging isn't the fault of the secondaries unless you've set them up to engage too early and they dump fuel before the engine can handle it. Also, if you're running a bigger cam or don't have your distributor degree'd properly or the primaries are too rich or you've got a low gear ratio (2.73) or your torque converter isn't right for your set up...any of these can cause your car to bog down. Try this: There's a little spring at the back of the carburetor that controls how fast the secondaries open. It has an adjustment screw and a set screw. Find those and tighten the spring about a quarter turn which will delay the secondary engagement. If the bog goes away you're on the right track. If not, you can reset it or even loosen it a quarter turn. If you buy a rebuild kit at your local parts store, it will have the instructions with pictures for performing this adjustment. The kits are pretty cheap.

Qjets get a bad rap but there is no other carb that's more adjustable. If you spend the time and set it up right you can get excellent gas mileage and awesome power...if you spend the time. Have fun!

 

what part of the secondaries should be at 90* The first half(toward the front) or the second half. The secondary blades on mine are at two different angles to start with, and I'm not sure which one to use to measure with. Also, are there any negative side affects from making it open wider, and what exactly are the good affects.

 

Hold on a sec. The secondary throttle blades are flat. They control the two barrels in the back of the carb, the bigger ones on a Qjet.

On top of the secondary throttle blades are the air valves, which look like throttle blades and are not flat.

The throttle blades are controlled directly by the throttle. There's a mechanism that keeps them closed when the engine is too cold, but after it's warm, your foot is in complete control of them.

The air valves are controlled by engine vacuum, more or less.
There's a spring and a diaphragm which controls the opening rate to prevent bog. They are opened when you open the throttle blades and the vacuum "sucks" them open. They open only as much as you need, which is why the quadrajet is more or less "one size fits all."

As far as I can tell, there is no disadvantage to having full throttle blade opening, because of the air valve.

The air valve doesn't open the full 90 degrees either, to prevent turbulence. There are other posts which explain how to get it to open more fully, and they explain it better than I can, and it's also in a tech article.