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 :)

mderoy makes a good point. I’ve seen the power valve hit the main body so many times I can’t count them.

Even had some power valve plugs hit the main body.

I always dry fit the metering block with the PV installed and no gasket. If it doesn’t hit you’re golden. If it does, then you need to clearance them main body or turn down the face of the PV plug in a lathe if that’s what’s hitting. Hell, you can even grind down the PV plug if you had to.

I have noticed that the PV gaskets have been getting thicker. If used with thin metering block gaskets, you can get into trouble.

Just an FYI FWIW