Well, apparently I have a magic garage that fixes things all by itself. I started down the list by busting out the multimeter and checking the battery. It looked good with the bike off, so I started it up and checked again. All good. Then I noticed that the whirring sound I had heard before seemed to be gone. I got my ear down there and sure enough everything sounded normal. So, I did a few throttle blips and it revved happily with no stutters or troubles. Amazed, I turned it off, waited a bit and repeated the process. I waited a while, started it up again and took it for a ride. Everything worked perfectly. I have no explanation, but I'm not complaining.