Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

an unexpected case of nozzle-drip

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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.

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