More nozzle drip big block 427 chevy

[chasrahm]

I bought Cliff's book in 2011 and some parts from Cliff's in January 2012.
The drivability of my Corvette is excellent from loaded in too high of a gear to WOT, car drives very well.  And it is very fast.
However, the exhaust note at idle is  very heavy and idle mixture never smells right.
After reading in the book and on this forum, I have nozzle drip.
First, I added back (unplugged) the idle bypass.  It helped, but not there yet.  Throttle stop screw is only half turn after contacting linkage, but I have drip.
The engine has high, even compression at 165-179, and could have a more aggressive cam, I don't know.

Recipe:
Idle tube .035
Idle channel restrictors  .046
Idle bypass. .092
Lower idle air bleed. .070
Upper idle air bleed  >.078 but <.093
Accel pump discharge .070. (Error?  I drilled these in 2012 and think it is wrong)
Main air bleed body. .070
Main air bleed horn. .070
Main jet. .071
Primary metering rod. 42B
Fuel inlet seat .125
Float level. .325

Thoughts?

[chasrahm]

In addition, my mixture screw openings are 0.90"

[77cruiser]

Do you have hole in the throttle plates? What's the vacuum @ idle? Does it flood at all on a hot start?

[chasrahm]

No holes in throttle plates.

Starts well when hot.  Hot or cold, I always have to pump the pedal a couple of times to prime engine with fuel, which I'm told is normal for a big block engine.

Vacuum at 650 rpm idle is 13-14.

[chasrahm]

What about my primary metering needles and the piston rod situation?
Could the spring below be too strong and not pulled down at idle?  Could this cause nozzle drip?
How to test my piston action?

[chasrahm]

Update:
I changed the idle bypass to .110"
Drove the car and still couldn't get the throttle plate closed enough to not have nozzle drip.

I pulled off the air horn and raised the float to .25". 

Did I just make it worse?  Really stinks rich now.  Lots of dripping nozzle.  Can't close throttle plate.  The idle speed screw is set about 2 full turns on the linkage.

Getting frustrated.

[77cruiser]

Lower the float to .375. How much fuel pressure do you have?

[chasrahm]

After reading and studying last night, I have to go back and mess / check with the timing.  In March, I installed a five speed.  Looking back, I wasn't present when my helper friend installed the distributor.  Car drives great, starts well, but I never checked where he set it.  Frankly, I haven't thought about it until now.
I'll report back later tonight.

[chasrahm]

So I've set the ignition timing,mostly by ear.  I'm finding the place where the engine runs best and vacuum is highest.  The engine jumps to life when started.  I then take it to 2,000 rpm and see if I can micro turn it to see if I pick up a few rpm.  Not much change.
At 1,000-1,100 rpm, my manifold vacuum has a very fast pulse to it and oscillates between 16-18.
As the rpm drops to 700, vacuum falls way off below 10hg. 
The vacuum advance is a B1 unit, a stock unit, giving 8 degrees distributor at 16-18hg.

So I used my vacuum pump to hold 16hg on the vacuum advance and started the engine.  It was idling at 1,100 so I slowly turned the throttle screw out to slow the idle rpms.  As it approached 700, I still visually the same amount of nozzle drip.

What to try now?

[ejowrench]

Follow cruiser77's advice and get a fuel preasure guage and LOWER your float level. Also check the condition of your float itself. Let us know what PSI you have at idle and 2000RPM.

[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