Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Idle problem
dlphil10:
Should I increase the DCRs to 0.055 as the next step? It definitely doesnt want more air. I loosened the tiny screw in the air horn over the air bleeds and it breaks up. If I unscrew it just a bit, I can get a little better response from the screws, but still not enough to get full rich indicated by a drop in rpm.
Cliff Ruggles:
I don't quit follow. If you open up the upper idle airbleed screw in the airhorn it will lean out the idle system. If the engine responds well to this and you start to see some control with the mixture screws then it's already got plenty of if not too much idle fuel.
What do you have the timing set at? Are you using vacuum advance? Manifold or ported vacuum?....
dlphil10:
Initial timing is set at 15deg, 13 vacuum advance(attached to manifold), 35 total (20deg mechanical). New DUI distributor with plugs gapped at 0.050". Idle vacuum is 18.5inHg in park at 900 rpm amd 15inHg at 700rpm in drive.
When I backed out the air bleed screw it did get worse, hut then backed out the mixture screw to compensate and the control with the screws seemed a little better. Unplugging a vacuum line makes it worse so it's not overly rich. Covering air horn chokes it.
Cliff Ruggles:
Why so much timing at idle? Few engines respond well to that much timing as it can cause an unstable idle and loss of control of idle speed and sensitivity with the mixture screws....
dlphil10:
I had it running at 12deg initial and the hesitation was a lot worse and it would backfire through the carb. I bumped timing to 15deg and acceleration is smoother in general. WOT is nice, tuning the air door opening rate is still a process but almost there.
I can still significantly slow the engine by turning mixture screws in. Manifold vacuum rises after about 1.5-2 turns out, (1turn out from lean drop) but then doesnt do much if I continue to unscrew the mixture screws. Should I be looking for a drop in rpm associated with being overly rich?
Also should I bump up the size for the accelerator discharge? It's currently sitting at 0.028"
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