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secondaries on a quadrajet

Babaganoosh

Babaganoosh

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For some reason mine do not open up. Occasionally they will, and it will throw me into the seat. I believe the quadrajet is a 650cfm on top of a 78 or 79 stock 350. If I ran the numbers off the drivers side could I find out? Do you guys think going to a 750cfm would help? Here shortly I'm going to be rebuilding one and would like some input on maybe "hot rodding one"


Thank You.
 
go to a book store and get a book on quadrajets thats the best advice I can give you. Also I think almost all were 750 cfm except for a couple on Buicks and Caddys that were 800 cfm but those are rare
 
I have a haynes manual that I have been reading here and there. I will do this with my Dad, although this is his first quadrajet he has built a few before.
 
I have the book you need. It is the best book on Q-Jets that I've seen. I picked up an extra one awhile back and I only need one, so I'll make you a deal on it.
As far as your secondaries not opening, it sounds like the secondary lock-out tang is not disengaging. Most often this is due to mis-adjusted choke or gummed up linkage. It is on the passenger side near the base plate and it rotates down to lock the pin that goes through the secondary throttle shaft.
 
Q-jets were either 750 or 800 CFM. Big blocks etc. got the larger carb which had slightly larger primary butterflies.

The secondaries shouldn't open under small loads (i.e. revving the engine in neutral).

My Qjet is not restricting my 400+ HP motor.
 
You can adjust the secondary spring tension on the opening of it , and you can adjust the lockout on the choke linkage .

You can change the rods and hangers and the jets too , but some of them are harder to find new now . I am collecting all the old ones I can score when I have money just to have parts .
 
Check the airhorn. If it is torqued down too hard, it can warp, and prevent the air flap on the secondaries to open. Air cleaner off, push down on the air flap. Should be a smooth movement against the resistance of the spring on the passenger side.
 
Engine size had nothing to do with whether they are 800's or 750's. You'll find lots of 800's on 80's Chev trucks with 305's, I've got or had a couple. Olds 307's had 800's as well.

750 is usually plenty even for a big block. Difference is in the primary side, not the secondaries.
 
from what i've read on the q-jet, the secondaries really shouldn't ever have a reason to open all the way on a sbc. they just don't breath enough to need that much air. i played with mine and got them to open a little slower so that i don't get that "blast off" feeling and end up trashing stuff offroad.
 
Thanks for the site. I have one that the 2ndaries are sticking open. I hope this will help. Maybe me and the original poster should swap parts:haha:
 
Ok, I finally had some time to mess around with it. The butterfly's are not opening at all. The linkage on the passenger side I can pull on it and they open. After talking to another guy I know, he said on the accelerator pump there is that bracket with multiple wholes with a rod connected to it. My rod is connected on the first whole, he said maybe if I put it on the 2nd whole( last whole one mine) that it possibly could open.

Thanks guys.

If i need any pictures to further explain what I'm talking about I can get them.
 
Be careful with this, there is a wide variety of accelerator pump lengths, if you move the rod, then floor the pedal, and the pump bottoms out before the accelerator pedal does, you'll break the air horn. Ask me how I know. :)

*When* don't they open? They won't in park/neutral (for the most part) and should hold shut even to moderate finger pressure while idling. With the vehicle off they should be easily workable with a finger.
 
As far as I'm aware they don't open in any gear. Today we tried it in park and they didn't open at all. I tried to force it open and it just killed the engine, I suspect why was because to much air feed in.
 
I always said I was going to try this, but never got around to it, now I don't have a running carbed vehicle. :)

Wire tie the secondary air valve so it can't open, (that's the upper secondary plates) then take it for a drive. See if it's any different. I suspect it will be a huge difference if they are actually opening.
 
If you do, report back what you find.

Another "test" you might try is to flip the air cleaner lid, take it for a drive, get on it, THEN wire tie the secondaries and pay attention to both how it feels and how it sounds.

I used to think the sound it makes when getting on it with a flipped lid or dual snorkels was the secondaries opening up, but now I notice that my TPI sounds almost the same. :) Haven't tried the flipped lid with my TBI rig.
 
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