At my wit's end

Have you ran the valve lash on that engine yet? The reason I asked is the '73 I picked up recently pulled the same stunt today.

It ran fine until it warmed up, then would waver up and down at idle. I turned it off and let it sit several minutes, and when I restarted it, it would idle down and sound like it was dropping one or two cylinders and then stall.

I adjusted the valves this evening and now it seems to be running smooth as silk. You may want to go ahead and do that before pulling your hair out over other ideas.