Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

More nozzle drip big block 427 chevy

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chasrahm:
My plan is to lower float back down a little to .375.
I'll install a fuel gauge inline between pump and carb.   I'm running stock mechanical pump.

What do you think about the power piston being too strong?  Ig it is up at idle, will that cause nozzle drip?
That might be the second step of the next test.  Pull the piston spring out and then start car to see if the lack of a spring at idle pulls them all the way down?

Thank you for your ideas!

von:
If you have an Airtex fuel pump from a chain auto parts store it probably has too much pressure for a Q jet. An AC Delco pump will have correct pressure. BTDT.

chasrahm:
I have performed a few more testing/tuning tasks to report:

At 700 rpm, my vacuum is pulling 8Hg. 

My fuel pressure is 6 psi at idle, drops a little as rpm goes to 1,500, then settles back around 6 psi.

I installed an Accel 31034 adjustable vacuum advance.  The vacuum line is non-ported tee'd into the PCV vacuum line.  My engine is really set sweet as far as ignition timing.  Stomp on it WOT and it goes frickin' quickly!  I have the vacuum advance set one turn off from a point where at steady light throttle, the engine will buck from too much advance.

But, at 700 idle, I have nozzle drip.  The idle screw is about 2-2.5 turns after making contact with the linkage.
My next experiment is to T (again) into the PCV line and use a fish-tank vacuum control valve to leak a little more air into the system to increase the bypass.  Hopefully, the rpms will go up and I can close the idle screw a couple of turns and see if the nozzle drip stops.

My bypass is currently 0.110"

thoughts?

chasrahm:
Ok, adding just the tiniest of vacuum leak, the rpms drop!
Page 29 of Cliff's book says two possibilities for nozzle drip.
First, not enough bypass. 
Second is too restrictive of an idle system.
So do I need to open up the idle tubes?

Cliff Ruggles:
A carburetor number would help.

The idle system is really lean, it most likely needs a LOT more idle fuel for what you are doing.

.070" accl pump discharge holes aren't going to work either, are you sure you are measuring the holes on the inner partition and not the outer one, which are around .070".

A .125" seat and .325" float level aren't going to feed a big block, at least not one that makes a lot of power in a pretty fast car.  You would need a really good fuel delivery system to keep the carb full on hard runs with those parts/settings.

The small seat and low float setting also effect fuel delivery, at idle and everywhere else, so also contributor to the poor idle quality with the big cam set-up......Cliff

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