A Mystery solved, maybe.
My bike was running erraticly again. No power, low end wasn't bad, but I couldn't get up to 60 mph without it spitting and missing. I couldn't figure it out. I had cleaned the carbs, checked the plugs, diddled with the CDI units. (By the way, sucks that there is no good way to test those, apparently.)
I changed the fuel, thinking I got some bad gas, no luck. I was doing some other things and got to looking at a sort of drain line that runs from the carbs and just hangs out the bottom of the bike. Looks like a vacuum line, but doesn't go anywhere. I pulled it loose from the carbs. The manual calls the part it connects to the Air Joint Pipe. I can't find any notation about the particular hose, though.
Anyway, when I disconnected the line the engine ran slightly better. I gave the Air Joint Pipe a hit of carb cleaner and things improved slightly. The bottom end of the hose was gunked up with old oil or something, I cleaned it out. Again, it seemed to serve no purpose, and with the engine running, it had no noticeable vacuum or anything. However, with it cleaned and reconnected, the engine ran fine.
It's a head scratcher. Anybody know the purpose of the hose?
The Shadow has been running fine since I cleaned it. Now I know one place to check if it acts up again, anyway, even if I don't know why it's there.