General Category > Quadrajet Carb Talk and Tips

Got it installed and running

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Kenth:

--- Quote from: GSP7 on March 03, 2025, 05:31:35 PM ---Like I said above,,,,, I was able to turn the APT screw all the way down and it didnt cause any issues at all, not even and "buck and surge" at all. It drove the same with the screw down seated, cept for the hesitation... Im wondering what's the deal? Its a 3/4 ton truck carb if that matters #17080213.
--- End quote ---

All calibration is based on the float adjustment.
What is your float set at?
#17080213 should be at 3/8".
If higher the mixture gets richer, if lower the mixture gets leaner.

And the APT starts rising the power piston at 2 turns up from seated.
3.5 turns up from seated is in fact 1.5 threads lift.

GSP7:

--- Quote from: Kenth on March 04, 2025, 02:43:26 AM ---All calibration is based on the float adjustment.
What is your float set at?
#17080213 should be at 3/8".
If higher the mixture gets richer, if lower the mixture gets leaner.

And the APT starts rising the power piston at 2 turns up from seated.
3.5 turns up from seated is in fact 1.5 threads lift.

--- End quote ---

Cliff told me to set the float level at 9/32-10/32. Its set at that
( I know carb specs say 3/8"(12/32) and that is what I set at previous rebuild at years ago)

Is the Float level set wrong?

I can screw down the APT screw all the way and it runs fine ( Orange PP spring used Cliff recommended)


Quadrajam-
Yes the hanger arms were checked for level/straight before install

Vacuum at idle it 15-17 (motor has RV cam, cam lobe centers int.105, exh.115, lobe separation 110)

Yes the vacuum advance is working

77cruiser:
A couple more degrees of timing might fix it.

quadrajam:
Float level is good. I recomend 73 jets and switch to the dark blue PP spring which
starts to lift around 9 inchs vac. 3-1/2 turns up on the APT. Been there, tuned that.

QJ
 

Kenth:
No increased rpm at "tip in test" with APT seated indicates a too rich mixture.

A too high float setting (too early delivery of fuel to the circuits makes a too rich mixture) and you may loose control of the APT adjustment.
Also too high fuel pressure will make the fuel level too high (same result, rich mixture).

No increased rpm with APT seated indicates a too rich mixture.

It is NOT a good idea to set the float at the same setting in different makes of the Quadrajet since the brass inserts in the center nozzle are different size in nearly every make, Buick, Cadillac, Chevy, Olds, and Pontiac all have their own nozzle sizes to start fuel delivery to the circuits depending on the demand from their engines.
Then you´ll have to calculate jetting depending on air bleed sizes.

As i said, ALL calibration starts with the float setting for the make of the carb that´s a candidate for a certain engine.

If correct float setting does not help, use a smaller main jet OR a larger primary rod to have the desired result.

"One size simply does not fit all, try walk a mile in your spouse's shoes."

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