Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Rebuilt 4988S Not So Good.

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Ozzmann:
Just finished rebuilding my Carter 4988S, with Cliff's kit, sitting on top of my 406 Pontiac. All I can tell you about the motor for sure is the cam is a Comp 270H Magnum, factory everything else it would appear.
I followed recipe #2
jets------------------073"
prim.rods--------------43
idle channels---------.053"
idle tubes------------0385"
upper idle air bleeds---.051"
lower idle air bleeds---.070"
idle air bypass-------.096
mixture screws-------0.96
sec. rods -----------Cliff's
main body air bleed-------0.70
main air bleed air horn--------0.70

Put carby back on car and it started pretty easy, but as soon as I started to adjust the fast idle cam, it died.
Would only run with the fast idle engaged, till it warmed right up. Didn't do this previously.
Once running I played around with the mixture screws, could wind one right in with no change, but as soon as I did this with the other mixture screw it died. After restart then both would kill the motor when fully seated.
If I wound them out too far the motor would stall??
Seemed happiest around 1 1/2 turns out.
I couldn't get car to idle without the primary throttle flaps slightly opened, as I had full vacuum at the vacuum advance port. This was the whole reason for the rebuild.
Anyway kept playing with the idle screw and mixture screws hoping to close the blades, but only managed to stall motor, then it wouldn't restart....just flooded I think.
Where Have I gone wrong, I know I stuffed up something. ???

Oh yea I also noticed a couple of times when it stalled when cold it shot fuel up out of the air horn about 4-5 inches into the air.

Cliff Ruggles:
Sounds like it is flooding.  Probably something between the needle and seat.  It's also possible that the incoming fuel was holding the float down. 

I see this once in a while testing carbs here on our test engine.  I shut off the fuel supply, then pulse the electric pump.  This does two things, it flushes the needle/seat, and allows the float to raise up and get control of the fuel level in the bowl......Cliff

Ozzmann:
I'm going to take the top off and just double check the float level and the needle and seat.
I pulled the small wire clip off, as you said in the book it's not needed.

Do you think the idle circuit is enough? I just can't get that ported vacuum happening.
When I pull the plug off the port pipe , the engine increases idle speed a lot.

Do I have a leak some where?

Cliff Ruggles:
You should have enough idle fuel with the specs given above.  You may want to go to .055 or even .058" with the idle downchannel restrictions.

The symptoms you describe indicate that you may have a vacuum leak someplace.  That carb set up has enough fuel for a pretty hefty camshaft.

What is the vacuum reading at idle speed?

Did you verify that the throttle plates are fully indexed and seated during the rebuild?.....Cliff

Ozzmann:
I haven't got a vac gauge handy at the moment, will have it back on Monday, a mates using it.
I was only getting around 10-11" at idle before hand.

The throttle plates did close and seated nicely during rebuild.

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