As you know, vacuum petcocks have been around a pretty long time. And of course these petocks have both a fuel and a vacuum line attached to them. Back when I was an instructor at Motorcycle Mechanics Institute (MMI) in Phoenix, AZ, we had a student get the two lines mixed up. Suzuki for a while made both hoses the same size, so this was more than natural to have happen. Well, she (yes, the student was a gal, if it matters) hard a hard time starting the bike but somehow eventually got it running, and everything was going just fine until, all of a sudden she was screaming, "fire!". Sure enough, the bike was on fire. But then things got even worse. In her panic, she managed to knock the fuel tank off the bike. Yup, you guessed it, now a sizable portion of the workshop was on fire, and she was running around in circles trailing flames from some part of her clothing! And then the instructor, trying to get things unde control, caught himself on fire! The day ended alright without too many more mishaps, but you can believe it when I tell you that most of the instructors tried to avoid this student from then on!