Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

an unexpected case of nozzle-drip

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Marx3:
I suppose a vacum leak ( like from several bad vacumlines ) would aid a case of drip?
I am experiencing drip on a completely stock 1975 Cadillac 500. carb is a 7045193 and yes, it has the 1-year only type of APT. Anyways, the carb is freshly rebuilt from shaft bushings, to DA rods for more secondary fuel.
I installed new idle tubes and sized them slightly bigger than the ones I pulled out. .036 or .037.
Other than installing DA rods, nothing is altered in any way.
Put the carb on the engine. Fired right up and ran stronger BUT the carb has severe nozzle drip.
Even with the idle screw completely backed out ( throttle blades closed ), the engine will purr right along at 6-700 rpm and the venturi's litterally shower the blades.
Thought the timing was too high, but it aint. It is a 6 degrees initial. I found that the VA actually gets full manifold vacuum, for some reason, causing the timing to be in the late 20's at idle. No wonder the nozzles drip, right...
So I unplugged the VA, expecting the drip to go away, but it didnt. Still some drip idling at 6-700 rpm and not much control over the mixture screws... I dont get this... ?

omaha:
yes that is a real head scratcher. A bad vac  line could add intake air [just like an idle bypass] that could be where the air is coming from for the engine to idle with the primaries closed. But a nozzle drip would indicate that air is coming from around the primary plates some how. after all, the fuel is being pulled from the plate area [i am assuming]. so that would leave me to believe that maybe the plates are not totally centered or they are not totally closed for some reason. I am really surprised that the VA is not a ported source. Of course if you have enough vacume signal to pull from the nozzles, maybe its pulling vac through the ported source from the plates also. Has this carb ever been messed with before. Is it all original? Put the carb up to a light source and look to see if the plates are totally closing. Check for cracks? {thinkin out loud here}.

Marx3:
I just rebuild the carb a week ago. installed shaft bushings and centerered the plates and everything.
I must say, I was not able to center the plates in such a way, that no light was seen. I can usually center them, so almost no light is seen around the, at all, but this one, I could bnot get any better, than a little light showing around each plate. But they are centered, so should theidle screw be backed all the way out, the plates will allow a little air to pass, but at least they are equally "open"

I was amazed too, at finding that a GM car from 1975 should have ported vacum for the VA.... NEVER seen that before.
The only ported source on the whole engine / carb is the one for the EGR. I am pulling the carb to check if the EGR source has the bleed off hole or not ( closing it if it has ).

Marx3:
The owner of the car told me today, that he has plugged the VA unit to the EGR port at the baseplate ( ported ) and plugged off all the necesary vacumsources. The car idles more stabel now, timing is at 8 degrees in idle and now it only one venturi that drips a little. Good news!
This means I gotta re-center the throttle plates, just to check.
But I sure am glad the drip has gone away in one venturi. Just didn't make sense the other day :-)

omaha:
...makes you wonder how the factory got them centered....some type of fixture  I would guess. If I remember correctly, each plate is made for its specific bore {I think} left and right. so they should not be mixed up. other than that I dont know the best method for the at home carb rebuilder to get them 100 percent. I guess practice..

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