The motorcycle lives! On my way home from work tonight, I bought some gasoline to clean Leila's motorcycle's gas tank with. Hosed down the inside with carburettor cleaning spray, hosed the carbs, then hooked the battery leads to my car's battery so we could use the starter motor, and it started!
Now, mind you, it's still going to need a lot of work. The lack of throttle response tells me the carburettors need more than just a spray of cleaning spray, and I find it pretty hard to believe that the spark plugs are still firing as hot as they did back in 1972. All of that's not too bad, even if we have to rebuild the carburettors (which I'll want to do eventually anyway, just to make sure they're operating as efficiently as possible). Most importantly though: the engine does turn over, and it'll even start and run for a little while. Feelin' pretty good about that over here, space cadets.