oddball

I'm back. Just want to know if I'm chasing my tail or if anyone has any ideas on which way to head. Background info at the bottom.
I've got the 403 idling relatively smoothly at 750 in gear, but that's around 1100 in neutral. Idle screws are out 5.5 turns and the O2 sensor says that's right about 14.5:1 in gear, but around 12.5:1 in netural. Vacuum is 12-14" at 750, more like 18" at 1100. When idling at speed, the engine pulls over 20" vacuum and swings really rich, which implies to me that the idle circuit is "rich", just not working well under the low vacuum.
The power piston spring moves at about 8".
Regular cruise is right at ~14.5:1, slightly lugging it leans out to 16:1 in a hurry. No detonation with a MSD 6AL-2 box.

Idle bypass air is at 0.059", idle tubes at 0.040", down channel at 0.057" idle air bleeds at 0.070". Main rods/jets 70/50B. Base plate as the external APT screw mod.

So it runs fantastically well, I'm just trying to get the idle more solid. Smaller air bypass (0.059" has been the smallest, keep breaking small drill bits in the set screws I use for replaceable bleeds....)? Other ideas? I've messed with the just about everything several times, willing to do more, just want to make sure it's not pointless.

General pointers on target A/F ratios would be great, too. I'm hitting 14.5:1 in cruise, aiming for 12:1 at WOT. 16:1 when slightly accelerating seems really lean, but I don't know if it's bad or not. And with the rest of the mix seemingly in good shape, I'm not sure what can be done about it!

Yes, I have the Ruggles and Roe books.

The build is a 403 with Edelbrock heads, KB pistons (final 10:1 compression measured) and an RPM intake, this is a 4MV QJet. Cam is a Lunati Voodoo 60803 (227/233 at 0.050"). Currently has a TH350. Can't remember what the torque converter is, but appears to have a ~2200 stall.

Thanks!

Octania

I have a similar engine with perhaps more cam [comp cams 292H]
I drilled idle air bypass to 0.099" and still don't get adjustability from the idle mixture screws.

What is this oxy sensor system you have to tell you the A/F ratio? Can you elaborate on that?

I thought the books recommended a difference of about 30 between rods and jets- but you run 20? My Toro 403 carb was at a difference of maybe 22- I forget the details- and I changed rods to attain a delta of about 30- like 75 jets and 45 rods. It seems rich based on the smel lof the exhaust but I don't have much better analysis tools at this time.

oddball

I got an Innovate O2 sensor and analog gauge. Just one, and I have isolated dual exhausts (there will be an H pipe down the road). Good setup for $200.
If I do a 30 delta then it's wildly rich. Looking at the stock calibration charts, Olds never had that much spread. I think the Olds setup is just different than the Chevy and doesn't need that much of a split. I read the same parts you did and started down that path, but it just didn't run right at all.

If I go with larger bypass air (I have set screws up to 0.110") then it just idles way too fast.