an unexpected case of nozzle-drip

[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..

[Marx3]

I always mark them left and right. As you mention, they do seem to fit their own side best.
I have actually never seen a baseplate, where the plates for this bad. Not on an untouched one anyways.
The carb does have those long mabs, that stock out onto the barrel. I guessing it has been remanufactured at some point?

[Cliff Ruggles]

A lot of timing at idle should actually lower the primary throttle plate angle and idle and help the situation, not hurt it.  Even with that said it's pretty easy to loose control of idle speed if the timing is too high and engine making too much vacuum at idle.

I've ran into this issue a couple of times on big CID engines pulling really hard on the carburetor at idle speed.   In all cases the carburetor also had pretty small MAB's making the nozzles very sensitive and pulling fuel from there easily. 

Float level is also a big player here, as a higher fuel level in the carburetor increases the sensitivity to the main boosters and allows fuel to flow to them easier. 

So for sure check the float level, and make sure the float isn't "heavy".  Fuel pressure can also be a contributing factor as well.  We've seen some fuel pumps lately putting out a lot of pressure and causing similar issues.

Also make sure the mixture screws are backed out sufficiently so it can get plenty of fuel from the idle system and not try to pull fuel from the main system to stay running......Cliff

[Marx3]

I once saw a Cadillac 500 that would nozzle drop like crazy, when the timing was too far advanced... it helped instantly to retard the initial timing.
This particular unit has pretty small MAB's... So this could be the problem?
I might just as well go .070 / .070 on the MAB's and put in 74 jets and 44 rods then...

Float was just replaced ( carb was rebuild with one of your S/R kit ). FLoat height was set at 1/4", and I even tried lowering it a bit. Didn't change anything.

I tryed making the lower IAB's smaller, using a punch and a checkball. Did get the holes noticably smaller, and upped the DCR's to .047. none of this helped.
Nozzle shower with the mixture screws 3 turns out. Still shower with the screws 4.5 turns out.
As for fuel pump: the pump is exaclty the same as before the carb was rebuild. Stock. Carb does not overfloat. needle/seat seems to hold the fuel pressure just fine.

All these things seem to be in order... thats why it is so weird.

On the other hand, the owner of the car complained that the engine was very shaky in idle. That was the whole reason he wanted the carb rebuild. Maybe this problem was also there BEFORE I rebuild the carb.

[Marx3]

I ended up increasing the tube size and DCR size slightly and making the holes under the mixture screws .075.
Nozzle drip is gone.
The specs for the idle system, were very small in stock form.
Like .033 tubes, .045 DCR, .075 lower iab / .050 upper iab, .040 bypass and mixture holes were around .045!!

Another problem has presented it self then... I can not get the idle down below 1000 rpm. The throttle plates are closed, the idle stop is far from contacting the screw.
Plates has been centered several times.
Take the car for a spin and it will idle at a lower rpm.

I covered the air flaps with a cloth and that didn't affect idle, so I am sure it is not sucking air past the secondary plates.

I can choke out the engine, by covering the primaries.
I don't get were the engine is getting the air. There are no appearent vacuum leaks.

[von]

Make sure there is loose play in the linkage rod that connects the primary and secondary shaft on the driver side. No play can mean the rod is holding open the secondary blades a hair.

[Marx3]

I can cover the secondary air flaps with a rag and it doesn't affect the idle. This leads me to believe the secondary plates are fully closed. Besides, I centered all four plates 2-3 times and the linkage is adjusted too.
Everything seems to be in order.

[omaha]

at what rpm does it idle at. Just wondering. PCV? Bad brake booster? Does it have bypass air?

[Marx3]

idles at 1000-1100.
Put it in gear and do some lively driving, rpm seems to drop to about 7-800. still with the plates fully closed.
The owner took the car for a nice long cruise yesterday and now it idles up around 1000 rpm again, but erratically.
I had a similar problem with a Qjet on a different cadillac 500 engine. also stock everything.
the secondaries would come off center, once the throttle had been stabbed, causing an erratical idle. I discovered it doing a last ditch attempt to cure the problem.

[77cruiser]

Is the throttle arm tight on the shaft?

[Marx3]

you mean the arm that the cable is attached to?
Yes sir. Nothing seems out of the ordinary...
I am getting the carb tommorow. Ill try a known working baseplate and see if that cures the problem.
Apart from this idle-problem, the carb performs perfectly.

We have had the engine idling with every vacum-appliance unplugged. PCV, brake booster, EGR, VA, transmission, heatriser, cruisecontrol, levelride, A/C, you name it.
Baseplate has .045" bypass