Vapor lock can only occur in a sealed system when fuel vaporizes under pressure. If fuel vaporizes in an open system like on a TW, the vapor is vented. Gravity will continue to pull fuel through any kind of air or vapor as long as the level of fuel in the source is higher than the top of the air or vapor in the system. Simple physics.
Now, if the fuel level in the source is lower than the air or vapor, no flow. That isn't vapor lock, that is air lock, which is different. Air lock occurs when a system is set up with a portion of it dependent on siphoning, and bubbles accumulate at the highest part of the liquid's path. Simple physics. I don't know how your Buell was set up, but if it had an air lock, it's probably because every time the needle opened in the carb a little air bubble made its way up the fuel line into the filter. Given enough little bubbles accumulating, an air bubble could easily break siphoning somewhere in the system. Kind of like a plumbing P-trap under a sink, but in reverse.
Anywho, is the bike in question running lean or rich? If it's running rich, turn the gas off while it is running, it will clean up, run fine for a minute, then die. If it is running lean, turn turn the gas off while it is running, it will not clean up and run fine, but it will still die.
