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Quadrajet question

Babaganoosh

Babaganoosh

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I have been battling with mine to get my secondaries to open, and tonight I think I have found the answer. I got to messing with mine and on the passenger side for the vacuum control there is a spring with a Phillip head(located in the picture) I tightened it up and now I seem to have alot more power and it has that sound of sucking in air. My question is, could this have been the cure to my problem?

Image1.jpg
 
I'm not familiar with that screw adjustment, but that rod going to the back is probably preventing the secondary flap from opening. There is also some link from the choke that keeps the seondary throttles from opening, but fortunatly that can be diagnosed with the engine off. If the spring/screw is also changing something else (like high idle speed?), you can adjust that linkage manually. Even the service manuals describe the method as simply bending the link until it is the right length.

I don't know what you've already tried, but it's good to have somebody step on the accelerator pedal while you verify visually underhood that the secondary throttle shaft rotates all the way to its stop.
 
Thats only one of the adjustments , that has vacuum at low rpm and blocks the door from opening at those times , you don't really need it if your door itself is adjusted to the right spring tension .
 
Paul, I know this would be kind of hard to explain but could you maybe perhaps explain what adjustments I could do? Or maybe point me in the correct direction?

Thanks guys
 
I assume the mechanical part of the secondaries (in the baseplate) open when you move to full throttle (i.e. nothing is binding).

My guess is you aren't getting the butterflies (vacuum controlled) at the top to open. Are you checking this at while the truck is just sitting there or are you guessing that they don't open when you're driving it.

The secondary butterflies shouldn't open unless there is a load on the motor i.e. even if you have it at WOT in the driveway in park the secondaries shouldn't open.
 
I'm guessing they don't open when driving. It doesn't sound like they are don't get that rush of air in like it should. After adjusting that screw last night it has more of that "sound".
 
I have been, haven't been able to find a whole lot. :o

Found something else to try, sounds like it will be the ticket. I ran across a guy with the same problem as me.
 
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If you don't find anything, let me know. I've got piles of Q-jets laying around, I might have one with the same vacuum break setup yours has, most of mine are the same vintage as the one pictured. If I took a look at one I'm sure I could figure it out.

I suspect that screw PROBABLY changes how soon the secondary air valve starts to open. I can't see what else is possibly connected to it, so it's a bit difficult to say.

A pic of the choke assembly side of the carb would probably do it.
 
:haha: I was right, now they come wide open and man does it sound good. :eek1:


adjusted the screw inside the linkage the pointer is pointing to.

post-1-1209176863.jpg


Not bad for a rookie, who has never messed with a carburetor. The best part is, countless people told my Dad and I that they worked fine. Even a master tech at a chevy dealership that has been there for 20+ years said I was wrong.




Now to pass a gas station. :doah:
 
You talking the flat head screw that is held in place with the set screw?

Secondary air valve tension adjustment. Good catch. :)

Keep your foot off the gas and your mileage will be as good as it gets for a gasser lol.
 
They need some adjustment, I think they are opening way to soon. I shot a quick video just because I was bored.

[youtube]T-Jpp8KIehg[/youtube]


here is the before video, man you can tell a difference.

 
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On the choke linkage there is a lever that looks like a "boot" that prevents the secondaries from opening when cold. It usually sticks and prevents the secondaries from opening when warm. I removed the "boot". This lets me control when the rear barrels open.
 
hmmm, I'm not sure if I have that piece you are describing, but I will take a look. I'm still fiddling with them haven't gotten the perfect "setting".
 
I'm running propane now, but I've always loved the "quadrajet sound" when you nail it, it kicks down a gear and the secondaries open... Sweet music.
on a side note anyone running a quadrajet baseplate with tha pane? doth it sound as sweet?:haha:
 
I personally have never had a problem with that "dogleg" but I know plenty have, so FWIW.

Just look at the passenger side of the secondary throttle plate shaft, there is a piece of metal pressed into the outside end of the shaft. The dogleg pivots on a piece cast into the carb body, just forward of the secondary throttle shaft as I recall.

edit: The secondary lockout is tied into the choke, so if the choke isn't working correctly, neither will the secondary lockout. Not many people understand the Q-jet chokes, and as a result, I've seen plenty of problems.
 
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Well today I wasn't paying attention and turned the screw the wrong way, instead of tightening I loosened. Now my question is, how would I go about fixing this?:doah:
 
We're still talking secondary air valve tension, right?

When I was doing them, I'd simply loosen it all the way (air valve would just hang open, engine off of course) then tighten, test, and continue. What I looked for was the air valve closing COMPLETELY, every time, without letting the spring use momentum to close the air valve, if that makes sense.

Adjust the air valve spring until the air valve closes via spring pressure, then press it open with your finger, and SLOWLY reduce finger pressure on it and see if it returns to the fully closed position. Repeat until it does. If you just jab it open with your finger and quickly release pressure, I figure that doesn't accurately represent most secondary operation while driving, and may not show it hanging up as it would if the air valve was slowly closing.

That's at least a baseline, although I never had a problem or bog setting it that way...if you feel there is, you can always go tighter, it's not hard to get back to the above setting. :)
 
Thats exactly how I set them. I guess when I wasn't paying attention the spring went all whack and now I'm not sure how to get it to go back on. I can sit there for days turning it and it wont tighten.
 
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