Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Smokey idle, and surging at cruise speed.

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Mudsport96:
Well, my hand got forced and I had to turn my project into a running vehicle over night. So I'll give the symptoms and hopefully somebody can point me in the right direction.

Recap the setup 76 Nova, 355 8.5:1 compression, comp high energy 268 cam 218@.050 on both lobes .488 lift with 1.6 rockers. Ported stock iron intake topped with a 17057229 carb. Has Cliffs HP kit in it with orange PP spring. Car pulls 14 to 16 inches mercury at 900 rpm.

SMAB .050
IDLE TUBES .035
DCR.050
MIX SCREW HOLES .077
Upper IDLE BLEEDS .074
LOWER IDLE BLEEDS .063
BYPASS .125
JETS 69
RODS 36B
SEC. RODS DR
HANGER H
SEC. FLAP SCREW @ 3/4 TURN

I had it out and cruising in drive at 35 mph around 1400 rpm it has a surge that I thought was a lean surge that seemed to get better turning up the APT. But I got to max adjustment, so I went to my parts bin and looked for some smaller rods and didn't have any. So I swapped out the 64 jets for 69 jets and left the 36B rods in place. The "surging" seemed to get a little better, but the idle is Smokey now and I can't tune it out. Do the main jets affect idle???
The surge doesn't fully go away while cruising at higher speeds either. It's noticeable at 55mph doing 2500rpm as well.

Mudsport96:
Ok, I put the 64 jets back in and the Smokey idle went away with no other adjustment.
So that leaves the surge at cruise.
Now, if I remember correctly, this carb originally had the 64/36B combo. And my engine is fairly mild so it shouldn't need much more than that I wouldn't think... right?

Mudsport96:
Alright, didn't get much done today with work, and.... the daughter driving the car into the garage door.
BUT! I wanted to try something, so I disconnected the accelerator pump and started the car. And I found that in park, from 800 rpm idle I can whack the throttle open and it revs super crisp to redline.
I have no visible nozzle drip at idle.
So I'm going to take a guess that my rods are too small. Any opinions?

Cliff Ruggles:
Yes, 36B rods are too small if you are using larger main jets in that carb number.

Verify that the power piston arms are level and EXACTLY even.  Call the shop when you get a moment and we'll get some larger primary metering rods headed your way. 

With a working APT system in one of those carburetors all you have to do is determine the most ideal jet size by doing some heavy part throttle driving, then fine tune the APT system for best light throttle/light load operation.

Are you using the vacuum advance?  How much timing is it adding at cruise?.......Cliff

Mudsport96:
The vacuum advance is adding right about 10 degrees. So all in total at cruise it's around 41 degrees.

But I think I have another problem. I checked the well plugs when I rebuilt it, and had no leaks. This weekend I disconnected the acc.pump and opened the throttle to look down into the manifold. And fuel was pooled in the manifold.  Removed the airhorn, and the bowl was empty, and there is fuel on the walls of the secondary bores along the bowl side.
So I took note of that and disassembled the carb and checked the well plugs again, no bubbles when pressurized.
Is it possible for fuel to leak out of the bowl to the manifold any other way, perhapse porosity? This was just 8 hours after the last time it was driven. So it is leaking down rather swiftly, and may be part of my idle tuning issue.

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