Never mind... that was weird.
I also noticed that the engine was running rough - touching the pipes indicated that one of the exhausts was cold. I measured with an IR gun after letting the engine run for a minute or two, and 5 of the 6 pipes were 46-48C, and one was 20C. Figuring that the problem wasn't air or fuel, since the next-door cylinder that shares the carb runs properly, I guessed it was spark. I swapped the spark plug with the next door cylinder, and now THAT cylinder wasn't firing.
So I put a new spark plug in, and now not only does the motor run much better, but the starter motor spins like a banshee now (??!!) Gotta love fixing a starter motor issue by changing a spark plug. I'm sure that there is a reason, but if I hadn't seen it with my own eyes I wouldn't believe it
I'm a happy camper! Boy does that engine sound amazing...