Fixed orifices wouldn't be on my list of things to change while dealing with fluctuating AFR numbers.
(1) Fuel level in the bowl at the trickle over point. I'd lower float level at the toe 1/8th to 1/4 inch and go for a drive.
(2) Check ignition timing at the cruise RPM where things are acting up. Could be weights, springs, or vaccum advance kicking in and out.
(3) Engine mis or skip at cruise RPM will skew AFR numbers. Dirty plug, plug wire, lean condition, rich condition can all cause a mis/skip. That's along with ignition timing being too high or too low for said cruise RPM.
(4) Fuel pressure going up with RPM could make the carb load up to the trickle over point.
(5) The AFR meter itself and wire connections.
Shoot for stable numbers and then fine tune
Clay
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