I used some starting fluid and it started and ran. Idled fine after it had warmed up.

All I could find was that the fuel adjustment nut on the rear carb had backed itself out and fallen off the collar. Weird. I did the "adjust out until the rpms stop rising" method when I tuned, I didn't think I had gone that far out.

So I put that back on, re-tuned, and also used this as a prompt to finally hook both carbs up to the choke. It was rear-carb only before.