I really wish I had paid more attention to the O2 values when did this years ago, but I didn't fully understand back then...
Do you remember TwoTired? If screwing it in too far causes a lean misfire, 02 values should be WAY high.
In my experience, screwing it inwards too far never caused a lean misfire (hollow tipped air screws), until the throttle was opened, slides raised. Then the already lean mixture drifted out of the combustion zone, the engine simply wheezed and produced no power until the slides were then lowered. The non-accelerator pump carbs need the idle mixture to be on the rich side, so that when the slides are raised the vacuum drop simultaneously reduces carb throat vacuum (the pull on the fuel jets, AND allows higher volumes of air to pass through the carbs. It's why you can't whack the throttle full open at low RPM, particularly under load. The hollow tipped screws always allowed some air bypass and prevented total shut off the the pilot emulsion process. During 70's development the EPA wanted better control/limitations over idle mixtures in the pursuit of cleaner exhaust emissions. As I see it, they first tried to placate the bureaucrats by making the air screw tips solid, making the control more effective at influencing the exhaust sniffer.
My analyzer is indeed a % CO indicator. No 02 sampling. But, I am NOT talking about taking an individual carb's pilot screw to extremes, neglecting the other three. But rather, turning them all inward (or outward) in the same increments and then monitoring the effect at the exhaust, the spark plug deposits, and the engine operational response behavior. I don't tune to shut off any of the cylinders, which might allow a cylinder to pump out raw inlet mixtures. In my experiment, I turned them all while sniffing just the one (of 4) exhausts. At 5-6 turns out, there wasn't much adjustment effect, and checking each of the exhausts, there was very little difference among them and any more tweaking was ineffectual. The engine ran wonderfully on the center stand, with hardly any plug deposits, but would pick up poorly when throttle was given. This became far worse when any sort of load was placed on the engine, making it un-rideable. Turning in the air screws all four at a time (to enrich the idle mixture) in increments gradually improved the throttle response. when it finally became street driveable, I check the turns count of the air screws, and it was right where the book stated to set them on a stock bike. I then started turnig them inwards (all four) and the throttle response got even better regarding how much twist I could give it in top gear from idle. To a point, as these air screws had that hollow tip air screw bypass. But, the spark plugs were collecting some serious soot deposits. They would only self clean with some high RPM drag style runs, to burn off the soot. Any prolonged idling and, god forbid choke, and the plugs would eventually foul.
The bike used was 74 CB550 K0, with 022a carbs. So, there could be an argument that 750 Carbs behave differently. However, no one has pointed out a pilot circuit design difference between the CB550 And the CB750 of that era. Indeed all the internal arrangements and passageways appear the same, apart from the obvious different casting mold.
Beware solid tipped screws can shut the air jet supply off completely, then there is no emulsion, and the throat vacuum pulls in only raw fuel from the pilot jet. I suspect this is why Keihin evolved the carbs to an IMS arrangement, as in the PD style carbs. These regulate the emulsified fuel final volume just as it enters the carb throat. With the PDs on the CB750, this allowed very lean mixtures during idle. It is also the reason why accelerator pumps were added to deal with the sudden slide opening from the mechanically linked twist grip.
