Dance steps, need some help!

[Cadman-iac]

  I'm trying to understand what the relationship is between the APT, the idle circuit and the main circuit.
 The APT seems to have an effect on both the idle and the main throughout the rpm range. 
  My idle mixture is slightly rich, it runs around 12.2 to 13.0, but I have a persistent lean condition just above idle that I can adjust out somewhat using the APT, raising it reduces the lean off-idle condition, but it also enriches the idle, and main circuit at all RPM's, in my opinion by too much.
 Currently I have the main AFR running around 14.5-15.5 at a cruise rpm of 2500-3000, but between 600 to about 1200 rpm at light throttle the AFR goes extremely lean, as much as 17.5 and higher, and I'm at a loss as to how to correct this.
 How do you richen up the off-idle mixture slightly and not change the higher rpm mixture?
 I've opened up the bypass air to  .095" from .039",and the IDCR's from .046" to .057", and the UIAB's from  .048" to .061" in an effort to get the idle circuit to work better in the higher RPM's.

 It's a delicate dance apparently, and i flunked out of dance class. Where do I go from here?

 Do I raise the APT, drop one jet size, and lean out the idle mixture slightly to compensate for the higher APT?

 This is a Cadillac Quadrajet on a SBC, #17057230, and it's got a main nozzle air bleed size of  .055, whereas the typical Chevrolet nozzle air bleed is only  .029. Would this be the problem, and if so,  how do you fix it?

[Cadman-iac]

 How big can you go with the IDCR's? I'm thinking about increasing these to see if it would eliminate this lean off-idle condition.
 Even the high idle AFR is lean when the engine is cold. I was just looking at the base plate, the idle transfer slots are not exposed at the base idle, and the AFR is good at that point if I adjust it, but doing this really makes the off-idle AFR go too lean.
 I've been going with a richer idle to get a less lean off-idle mixture. Now im thinking that is the wrong approach.
  Is a bigger IDCR the better way to correct this, but how much bigger?
 I believe if I use bigger IDCR's, I can reduce the idle mixture screws to compensate for the increase in available fuel, and the increase in available fuel should correct this lean condition.
  Or do I raise the APT and drop a jet size  and increase the idle mixture screws?
 Just thinking out loud here, so to speak.

 My sincerest appreciation for any help here, thank you. 
  Rick

[77cruiser]

I'd go back to .048 UIAB.

[Kenth]

IDCR are plenty large at .057", as are .040" idle tubes.
(I would look for .052" IDCR with .038" idle tubes with the .061" UIAB.)

Set APT by the "tip-in" method at 2200 rpm´s and let it be.
Set idle mixture screws one half to one turn further out and i guess you´ll be good for now.

JMHO

[novadude]

I think those caddy carbs have large lower idle air bleeds.  I wonder what would happen if you reduce those a bit to ~0.062?  This is just a "what if" question.... I can't say that this will fix your issue.

Seems to me that just off-idle, those holes (and the top of the transfer slot) would be adding air to the mixture coming from IDCR.

[Cadman-iac]

I'd go back to .048 UIAB.

 That's not as easy as it was to enlarge it. Not sure i have the resources to do this. Gotta look at my options.
 Thanks for the suggestion.

[Cadman-iac]

IDCR are plenty large at .057", as are .040" idle tubes.
(I would look for .052" IDCR with .038" idle tubes with the .061" UIAB.)

Set APT by the "tip-in" method at 2200 rpm´s and let it be.
Set idle mixture screws one half to one turn further out and i guess you´ll be good for now.

JMHO

 Kenth,

 I tried  .061 IDCR's but it didn't work, just seemed to raise the problem to a higher rpm.
 I've got a lot of various sized restrictions, so going back to a smaller one is not a problem.
 I've also got a lot of different idle tubes, so that's no problem.
  I'll go back to those sizes and see what happens.
 Thanks for your help.

[Cadman-iac]

I think those caddy carbs have large lower idle air bleeds.  I wonder what would happen if you reduce those a bit to ~0.062?  This is just a "what if" question.... I can't say that this will fix your issue.

Seems to me that just off-idle, those holes (and the top of the transfer slot) would be adding air to the mixture coming from IDCR.

 Yes, the lower idle air bleed on this one is at  .078, and i haven't made any changes to those.

 I was just wondering about going back to the original size on the bypass air passages, I have the means to do that.
  I'm not sure where i saw that the small bypass passages were too small, I went through all of my posts and threads looking for it.
 There are several suggestions to enlarge the discharge ports.

 Would small bypass air passages be a fix?
 I thought i was figuring things out, now I'm not so sure.

[77cruiser]

A smaller IABP would help. Making the LIAB smaller would help too as Novadude mentioned. Some are successful at peening the holes then drill to size. I just drilled & tapped for 6-32 brass set screws.

[novadude]

I've peened the lower idle air bleeds from ~.078 down to ~.06x before using an old accelerator pump check ball and a punch (and then qualified both with a drill to the same size).  It's not the easiest thing to do, and the casting ended up looking ugly, but it's one way to address this.  I don't have any before and after comparisons, as it was a new build and I was changing multiple things at once on this particular carb.

Setscrews as 77cruiser suggested would probably be a better idea.  I wasn't sure if I could get a setscrew in there that was short enough so that it wasn't blocking the part of the down channel leading to transfer slots and idle discharge. 

[77cruiser]

I think I used 1/8 inch long set screws, I don't think they are blocking the channel. Something I might have to check someday.

[Cadman-iac]

A smaller IABP would help. Making the LIAB smaller would help too as Novadude mentioned. Some are successful at peening the holes then drill to size. I just drilled & tapped for 6-32 brass set screws.

 I found a post you made with a link for McMasters, but it didn't go specifically to those setscews, and trying to find them on a phone is a bit difficult.
 You wouldn't happen to have their part number or item number handy would you? I'd like to order some for this.
 Thanks,
  Rick

[Cadman-iac]

I've peened the lower idle air bleeds from ~.078 down to ~.06x before using an old accelerator pump check ball and a punch (and then qualified both with a drill to the same size).  It's not the easiest thing to do, and the casting ended up looking ugly, but it's one way to address this.  I don't have any before and after comparisons, as it was a new build and I was changing multiple things at once on this particular carb.

Setscrews as 77cruiser suggested would probably be a better idea.  I wasn't sure if I could get a setscrew in there that was short enough so that it wasn't blocking the part of the down channel leading to transfer slots and idle discharge.

 A few years ago I had an old E-Jet that I used to practice on with some of Cliff's technics, and I tried making the lower bleeds smaller using the checkball and punch method, i wasn't happy with the results. So I've been hesitant to try again.
 I did successfully plug and re-driill the bypass air passages on a base plate using some 1/8" aluminum welding rod.
 I was thinking that if you could drill the lower bleed hole larger but not go deep enough to go through to the passage behind it, so that there's a shoulder to stop your plug from going too deep and blocking the downward channel, then you can use a piece of aluminum rod and re-drill it to the size you want.
 The problem with this is that there's not enough thickness around the bleed holes.
 I like the set screw idea. It wouldn't matter if you got into the downward channel a bit with the drill or the tap so long as the screw doesn't go in too far. A bit of Locktite would keep it in place.

 My other problem is I don't have a good selection of small drill bits. Where do you guys get yours from?

[77cruiser]

I get drills from McMaster Carr too. Set screws only come in packs of 50 the small ones anyway.
https://www.mcmaster.com/products/set-screws/set-screws-2~/thread-size~6-32/length~1-8-1/material~brass-1/tip-type~cup/

[Cadman-iac]

I get drills from McMaster Carr too. Set screws only come in packs of 50 the small ones anyway.
https://www.mcmaster.com/products/set-screws/set-screws-2~/thread-size~6-32/length~1-8-1/material~brass-1/tip-type~cup/

    Thank you for that, I'll get some ordered ASAP.