Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

idle issues

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wcumagic:
Alrighty then!  Its nice to have a quadrajet only forum with experts about!  I have recently purchased and read Cliffs book, with a few questions yet unanswered!  Here is my setup, more to understand!  (make sure I didnt screw up somewhere)

1996 Lt1 350 with Aluminum heads “Gone through” by Barnes and Reese Racing (everything done) breathing through headers and suckin fuel through a good ol' quadrajet and GM performance intake.  3:73 rearend with a 5 speed totin' around a 1989 camaro Iroc-z.  I have a Comp cam  with duration at .050 @ .218 and .224 with valve lift of .495 and .502, but I think that changed since I have put 1.6 ratio rockers on it since.  I have the factory fuel pump with a nice mallory regulator holdin' it to 6 psi.  With Cliffs book, I have taken my quadrajet ( number 17057230) and done the following mods

idle mixture holes   .090
idle bypass air    .080
idle tube      .037     (pita!!!)
idle down channel    .052   
upper idle air bleed    .070  not in air horn
lower idle air bleed    .077
idle by pass air    .080
no plate holes

fuel inlet       .145   
smaller float installed
main jet       .072
rod.         .042 with .025 tapered tip
secondary hanger   G
secondary rods   CE
longer power piston spring installed (yellow in edelbrock kit)

Questionably, I didnt see mention of actual float height or how to measure it – have since found info and set it at 5/16”

My main question is my idle – it idles well at 1000ish, but every little bit it jumps to 1200 and my vacuum stays about 10 until it jumps and then it jumps to about 12 or 15.  I cannot seem to get the idle screws set right because there doesnt seem to be a sweet spot where the vacuum stops gaining when adjusting it. 

Its possible its because of the throttle shaft bushings, but I had a hard time finding any info on what are acceptable tolerances.  I have enough vertical movement to hear a rattle when I shake it, and enough side to side movement to go about 1/16 or possibly a little more.  Is there a way to test to see if that is indeed what the problem is, or do you see another issue?  I didnt have a problem with finding idle before the rebuild, so thats my reasoning for not replacing the bushings this time through. 

I test drove it today and its nasty, I have a lot more midrange torque and I no longer have traction in first gear.  The secondaries open up much earlier now with no bog, only when I rev the poo out of it.   In other words, previously they opened up near 6000 rpm only, but now with a slow pull from 1k to 6k they didnt open, but a quick jab at 3k made them open and sing their evil song.   I'm concerned about the idle though, and although I love the smell of rich carburetion, I dont want to damage anything by running it too rich or even too lean at idle.  I have the screws set now at 2 turns out per.   Thoughts?

wcumagic:
forgot to mention heads shaved to raise compression as much as Mr Barnes could, so I have to run 93 or better. 

Cliff Ruggles:
Check the distributor.  It sounds like some of the mechanical advance is coming in, causing idle speed to fluctuate.  The timing needs to be rock solid at idle speed.

I would also think with that engine/cam combo you could easily idle it down to 700-750rpm's......Cliff

wcumagic:
The mechanical timing doesnt start advancing until 2k to 3k.  12 degrees advance idling (up to 2kish) and upon revving it goes to 36 degrees. 

I could idle down before the carb build, I just havent gotten that far yet.    ::)   

So what do you think about acceptable tolerances on the throttle shaft?  Can it run too lean at idle and would that cause this?  Would a small vacuum leak cause fluctuation?  ???

omaha:
   I'm thinking that the power piston spring that you put in there is too stiff to keep the rods down wile idling. (it might be overcoming the low vacuum during idle). you might try leaving it out and see how it idles just for a test. or find a really light spring to put in it. (maybe the orig?)
bushings could cause some fluctuation true but, you said that this prob started afdter the build so that kinda negates that theory. I'd still put the bushings in it though, cant hurt. I'd advance it just a bit on the initial timing and see if that has any good effects. If it dont, just put it back where it was. Float level seems ok, Cliff recommend 1/4 but I dont think where you got it will affect the idle much. Small float;did you check it (for leaks) {i am sure you did} Just a possibility (small one). I am not fond of the FI fuel pump of the original z-28. Weren't they like putting out 44 psi? Kinda alot to regulate down to 6 psi (unless you got a real good bypass on it). I think 15 psi pump would be better. Something happened between when it was idiling good and now. so it must be something that was changed or some thing that went bad from then to now. Oh well, just my 2 cents worth. I am not the tuning guru like some of these drag racers like Cliff.      Hope you figure it out.  Until then; have fun anyway!

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