Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Asking for Setup Help Please

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Shiny:
I have a carb apart to deal with a flooding issue after sitting for 10 years with little use.

When I set it up, I made some tuning decisions that may not have been the best.  I did use a Cliff kit at the time and had read his book over and over.  I remember Cliff recommended the primary jets.


Please review and comment before I put it back together.

Do these numbers and parts sound reasonable?

70 Pontiac 350, stock low compression, Summit 2800 cam, dual exhaust

At sea level now, will be moving back to 4500 feet.

69 Buick Quadrajet       29240MD

Measured:

Upper Air Bleed      0.053
Down Channel      0.049
Lower Air Bleed      0.079
Bypass         0.089
Mixture Holes      0.090

Chose:

Idle Tubes         0.035
Primary Jets           70
Primary Rods         44B
Secondary Rods          CH
Secondary Hanger         O
Power pump spring          8"  (Yellow)

Float at 5/16"


Appreciate any and all guidance on these choices while I've got the carb apart.

Cliff Ruggles:
Why do you think the tuning decisions aren't the best?  How does it work?  Idle?  Transition off idle, light throttle cruise, heavy part throttle, full throttle, etc?.....Cliff

Shiny:
I think my decisions were bad because they ended up not working!

I can't get it to idle well.  Car is not a driver so can't answer beyond that.  It revs up and runs smoother when I open the throttle, but that doesn't tell me anything.

Immediate problem is the idle.

After putting it together yesterday, it ran OK when I first fired it up with choke closed.  Here's a video:

https://1drv.ms/v/s!AiIRc33Ia4jVg-cGVFINy01y57Ju6A

After warming, I had to open the primary blades to keep it running.  I can see gas coming out of the upper nozzles, which tells me I have too much air down the venturis to be running off the idle system.

I tried opening the needles and closing the blades, but could not get it to idle without the "drip".

I put my hand over the air horn and it picks up rpm, sounds smoother.  To me, this means it wants more fuel from the idle system.

I checked the timing, set it at 9 degrees.  Starts OK there.  Vac advance added quite a bit.. I'm guessing is at 20+ degrees at ~700 rpm, but won't idle with or without that advance.  Manifold vacuum was pretty high, maybe 18", but erratic as the idle was rough.

I turned the needles all the way in and it stumbles bad, so I'm sure it's getting some fuel through the needles.  It just doesn't get a lot better when I open them.  I can open them almost until they fall out and it doesn't pick up rpm.

Here's a video showing as good as I could get from the nozzles when its warm.  You can tell its running rough and see the gas coming out the nozzle:

https://1drv.ms/v/s!AiIRc33Ia4jVg-cAG6wC0BqD7M3yNA

If I'm reading this right, what changes are likely to fix this?

More information on my PY Forum thread, including some tuning suggestions by Kenth.  Thread is here:

http://forums.maxperformanceinc.com/forums/showthread.php?t=818909

Carb does have APT, but I don't have any dialed in.  I'll try using it to raise the rods and see if that has an effect.  Maybe I'm just starving the idle system at the jets by not having any
APT dialed in?  This doesn't make sense to me, given the drip from the primaries..

Shiny:
Today, it started fine, wasn't too bad when choked.

I screwed in the APT adjust, but it didn't perform any miracle for the idle.  It did seem to make it run worse above idle on the primaries, which would be consistent with it richening up too much.

Should I expect the APT to affect idle or not?

Cliff Ruggles:
The APT system doesn't adjust the idle fuel it raises and lowers the metering rods so will only effect light load at part throttle.

The symptoms indicate it needs larger idle tubes and DCR's.  .089" should be enough bypass air for the small cam in the 350 engine.

If you can get it to smooth out and speed up by tipping in the choke flap and or putting your hand over it and richening things up they start there and don't add any more bypass air until you have full control with the mixture screws.

.037" idle tubes should be plenty provided the idle airbleeds didn't get opened up.  I'd try .055" DCR's and see if that helps?......Cliff

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