AFR slowly richens at idle

Yes, my t-slots are correct and I have additional bypass air (via the center stud). My ignition timing is not causing the AFR to get slowly richer while idling until it dies. Let's keep focused on what has changed since Friday...

It's also very unlikely that power valve interference to the metering blocks would have suddenly started - that would have been obvious on assembly. Also using a genuine Holley PV which is "supposed" to clear. But an internal gasket leak is a possibility (reusable blue gaskets).

The most likely suspect is a creeping fuel level from a dirty or sticking needle & seat. I'll check that this morning, then start looking for zebras instead of horses :)