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Author Topic:   Q-jet tech
posted May 01, 2001 10:33 AM
A good starting point for the first-timer would probably be one of the Rochester books such as the one by Doug Roe calld "Rochester Carburetors". has it. There's others as well, but that's just one that comes to mind as a good source for baseline stuff for the quadrajet.
If there's any specifics you want answers to for your application, just hollar at me here or PM me, or email.
Always glad to help out where possible.

Kinetic Performance

posted May 01, 2001 11:00 AM
Hmmm....good starting point, but I'd have gone a bit higher on the hanger letter for your app. On the jets, rods, etc. there's some areas there that are somewhat forgiving, since the Quad operates as more of an air valve that is variable based on the needs of the motor, it is able to make jet sizes and rod diameters work for more applications. Now, if that isn't a general enough statement...LOL!....anyway, your 406 is likely to want a bit more of a pump shot, and unless they enlarged the pump well to accept the larger, 2bbl-sized, pump as well as lenghtened it's duration, the worst case could be a bit less "boost" than is needed from the pump squirters for your motor.
You didn't list some of the other mods that may or may not have been done, like secondary air valve work/timing, primary side squirter sizing and fuel well improvements as well as air bleed work, and main feed tube mods, but it looks like what ya have there is a good, usable carb, that is set up to fit as many applications as they can.
that's sorta what a lot of builders will do - build as few "custom-made" carbs as they can and stick with basic (stage 1, stage 2, etc) models that they try and "fit" to as many different engine combo's as possible.

Is there some symptoms the carb is displaying that leads you to believe it could be better set up for your engine combo?

Let me know and I'll try and suggest some tricks to try.


posted May 01, 2001 12:49 PM
ok, first, I'd soften the secondary air flap spring, so that there's almost zero tension when they are closed. That's one of the causes of that sluggishness, since they're probably not opening soon enough, but that is also an area where fine tuning varies from motor to motor, based on the manifold vacuum signal each motor has.
you could work a little with leaning the primaries, but not much gain will be seen there, since on restarts, you are almost always 90% off of the primary circuit anyway.
Another thing to do is to drill four .030" holes in the secondary fuel feed tubes, maybe 1/4" down from their ends if they're not already there. Just drill them right thru both sides. This will help with a smoother transition on the secondaries.
You also may wanna make sure the secondary butterflies open just a tick PAST 90 degrees, and that the secondary air flaps do open fully 90 degrees.

Just some random thoughts...hope they help...


[This message has been edited by KPLugnut (edited May 01, 2001).]

posted May 01, 2001 02:04 PM
Thank you much for the help KP!!

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