Cliff's Quadrajet Parts and Rebuild Kits

  I couldn't sleep tonight thinking about this carburetor, so I was posing some questions online for AI to answer and here's what I've learned.

In a Rochester Quadrajet carburetor,

the main nozzle air bleed is effectively the final stage of air bleeding, where the air/fuel emulsion is discharged into the venturi, while the upper and lower main circuit air bleeds (also known as emulsion bleeds) are earlier stages that control the initial mixing of air and fuel within the main well.

Difference in Function

Upper and Lower Main Circuit Air Bleeds (Emulsion Bleeds): These bleeds are located within the main well of the carburetor body and air horn. Their primary role is to introduce a calibrated amount of air into the fuel column as it rises from the main jet, creating an emulsion (a mix of air and fuel). This emulsification helps to decrease the fuel's density, promotes better vaporization, and helps "lift" the fuel into the airstream. The size and number of these bleeds shape the fuel curve in the mid-to-high RPM range by varying the air mixing as the fuel level in the well changes with engine speed. The upper bleeds have the most impact, while the lower ones have less effect.Main Nozzle Air Bleed (Discharge Nozzle): The final discharge nozzle (sometimes referred to as the "high-speed bleed" in a general sense, though it's the exit point) is where the air/fuel mixture exits into the boost venturi. While the entire passage acts as an air-bleed type system, the primary function at this point is to discharge the already-emulsified mixture effectively into the high-velocity air stream in the venturi. The final bleed size here fine- tunes the very top-end, full-throttle air/fuel ratio.

Effect of a Larger Main Nozzle Air Bleed

A larger main nozzle air bleed (or increasing the size of the final high-speed bleed restriction if applicable) introduces more air into the system or modifies the discharge pressure characteristics. The general effect is a leaner air/fuel mixture, especially at higher engine speeds and loads.

Leans the mixture: More air mixing with the fuel reduces the overall fuel density being discharged, leaning out the mixture.Reshapes the fuel curve: Air bleeds affect the shape of the fuel curve across the operating range, rather than just shifting the entire curve up or down like a main jet change. A larger main nozzle bleed will lean the mixture primarily in the upper RPM and high-load ranges.Delays system activation (to a degree): Larger bleeds can slightly weaken the vacuum signal in the fuel well, potentially delaying the point at which the main system fully activates or becoming more sensitive to engine load.

Pull-Over Enrichment System and Air Bleed Size

The Quadrajet's main metering system uses tapered metering rods that move in and out of the main jets based on engine vacuum (controlled by a power piston). The rods are pulled down into the jets by high vacuum (lean cruise mixture) and rise out of the jets under low vacuum/heavy load (rich power mixture).

 More to follow, too much for one post.

  Yeah, I've gone through the instructions on this AEM brand AFR gage forward and back several times looking for anything on a required calibration, or a recalibration, but it's not there.
 The only so called calibration necessary is if you want to run a different fuel, apparently it has different tables and there's a switch on the back to select whichever fuel you're using.

 And yes, I'm running the float at 13/32. I had tried a higher setting previously, 9/32, that's been about a month ago now, but after reconfiguring it this last time I set it back to stock.  I was trying to eliminate any variables from previous modifications and basically start over but with improvements like the relocated UIAB's and replaceable LIAB's.
 I suspected that it's necessary to recalibrate for the new location of the UIAB's but wasn't sure, but you guys confirmed that for me and I appreciate that,  thank you.
 I haven't had a chance to do anything else because my wife has me doing "honeydews", which is ok, I'm waiting for parts from Cliff to show up.
 

Something else I just noticed.  You are using the stock float setting of 13/32".  I've typically used 9/32 or 10/32 on all the M4MC carbs I build.  Have you tried experimenting with float height at all?  Are you certain it is 13/32 and it didn't get knocked lower during calibration changes?

I don't get that. I have an Autometer & a Innovate the Innovate just uses a free air check if it shows 21% O2 it's good.Can't remember what the deal was on the Autometer.

Here's the chart for the calibration options for the AFR gage I'm using. As i understand it, the default setting is the one that shows the AFR readings that we typically use.
 If you see something I missed please let me know. Thanks, Rick