Actually Mike, it isn't vapor lock,it's a vacuum lock. You can get the same effect by sucking on a plastic straw and pinching off the open end of the straw. Vapor lock is when you have a volatile liquid (ie gasoline) in a line and it gets heated to its boiling temp. The liquid begins to bubble and the bubbles won't flow thru the line.
Sorry to get so anal, but it's Saturday, it's early and I haven't got enough caffine in my body yet! lol