General Category > Quadrajet Carb Talk and Tips
Relocating the UIAB, are size adjustments required?
Cadman-iac:
--- Quote from: Kenth on October 28, 2025, 01:01:27 AM ---What engine?
--- End quote ---
Sorry, it's an 88 Chevrolet 350 with the stock swirl port heads, I think they're number 193's, have to check again to be sure. Also has 4 relief flat-top pistons and the thicker composite gaskets, so compression is about 9.0:1 maybe a bit less, not positive.
The carb also has the larger .055 main nozzle air bleeds, and i have no idea how this plays into the combination. It's a 1977 Cadillac 425 carb #17057230.
I've been trying to set it up like a typical SBC carb, but the nozzle bleed size changes the equation, unfortunately I don't know in what ways.
Is this something to worry about or just ignore it?
novadude:
That sounds like a LOT of idle fuel for a stock-ish SBC. Are you saying it is still lean at low RPM part throttle? See my idle calibration above... this is a 9.6:1 355 vortec head SBC with a 270/278, 217/225, 108 LSA cam. Light throttle, low RPM A/F is in the 14s with no lean surging, etc. My idle tubes are much smaller than yours.
I wonder if you are on to something with the theory of .055 MAB at nozzle significantly delaying the start of the main circuit? My carb is a 17080204, so it has the Chevrolet 0.028 bleed in this location.
77cruiser:
I had a carb several years ago that was acting up at light throttle & found that I had put the wrong base to main body gasket in it.
Cadman-iac:
--- Quote from: novadude on October 28, 2025, 08:16:12 AM ---That sounds like a LOT of idle fuel for a stock-ish SBC.
--- End quote ---
Yeah, going by the AFR gage as I'm opening the throttle, just over idle up to around 900/1000 rpm, it goes lean, as much as 17.5-18.0, and I'm afraid that is too lean. If you hold it steady when this happens it'll stay in that range.
I went through it today and changed the UIAB's to .044" and the idle tubes to .032".
Here's the setup as of right now.
Idle tubes................. .032", stock is 035
Chnl restrictions....... .046", stock is 046
UIAB, relocated......... .044', stock is 048
LIAB.......................... .061", stock is .078
Bypass air................ .045", stock is .039
Idle discharge......... .088", stock is .052
Float.........................13/32, stock is 13/32
PAB-Body................. .040", stock is .040
PAB-Horn................. .070", stock is .070
Main noz. bleed. .......055", stock is .055
Main jet..................... #72, stock is #72
Primary rod.........#44J, Cliff's stock is #52P
PP spring.............3-10" blue, stock 3-10"
APT set.................3 turns, stock 2 ¹/⁴
Ac pump noz........... .025", stock is .025"
Sec. Rods....................BA, stock is DS
Hanger.........................K, stock is T
I haven't driven it yet, but I've got an appointment tomorrow morning in Tucson, so it'll get a 240 mile run. I'll get to see how well it does with this newest setup. Hopefully it will be better.
I've checked and double checked the base to bowl gasket, it's correct.
I want to thank you guys for helping me try to figure out where I went wrong. I really appreciate the help Novadude, 77cruiser, Kenth, thank you.
I'll let you know what happened when I get home.
Rick
novadude:
That looks like it should work great in a mild 350. Report back and let us know the results. It seems odd to me that you were having issues with the old combo, as that should have been plenty of idle fuel with the 0.048 main body IAB and .040 tubes. I wonder if you are getting some kind of air leak somewhere in the idle circuit?
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