Relocating the UIAB, are size adjustments required?

[Cadman-iac]

  Just a quick question, i just relocated the upper idle air bleeds on my carburetor, but I was wondering, because of the new location and the different route that the air takes to get to the original bleed location, do you need to resize for any reason?

 The air now runs through the air horn to the gasket where it needs to do a small zigzag in order to continue on down to the channel restriction, whereas before the air entered just above the restriction.
 However, because of the new location (on the top of the horn basically), there should be less of a flow hindrance as the air is coming at it straight-on, a sort of ram effect so to speak. The original bleed location being next to the venturi and aiming slightly downward, does not get any "ram effect".
 So do the two issues cancel each other out and there's nothing to worry about, or are these something to be concerned about? Just curious.

 Rick

[Cadman-iac]

Here's a couple of pictures showing the new location of the upper idle air bleeds and the primary air bleeds in the air horn.

And a couple more showing the plugged original UIAB.

[novadude]

The air horn UIAB will typically need to be smaller than the main body, indirect UIAB.  On my current carb, I am running a 0.040 UIAB (air horn with screw in bleed like yours), 0.062 LIAB, 0.029 idle tube, and 0.046" IDCR.  Plenty of fuel for a nice idle with a 217/225 @ .050, 108 LSA cam.

[Cadman-iac]

The air horn UIAB will typically need to be smaller than the main body, indirect UIAB.  On my current carb, I am running a 0.040 UIAB (air horn with screw in bleed like yours), 0.062 LIAB, 0.029 idle tube, and 0.046" IDCR.  Plenty of fuel for a nice idle with a 217/225 @ .050, 108 LSA cam.

 Right now I've got the UIAB's set at .048 in the new location on the air horn.
 I also reduced the LIAB's to .061 from the stock size of  .078.
 I changed the IDCR's back to .046, which is the original size.
 The idle tubes are now at .040, but are still larger than stock which was .035.

 I'm running a Comp Cams HR with 206/210 @ .050, with an LSA of 112, so it's got a really smooth idle and pulls well, much better than the original flat tappet TBI cam did.

 If I reduce the UIAB more, just how far should I go, .044?
  Should I change the idle tubes back to the original size  .035, or am I ok with where I'm at now?

  Rick

[Kenth]

What engine?

[Cadman-iac]

What engine?

 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.