And if you are REALLY good, you can pull in the clutch, pull the key out of the ignition, pop the gas cap open, put the key back in, start it back up, and take off again, BEFORE you completely stop. Yes, it really can be done and I have, along with a couple others on this forum, seen it done, while traveling at 70+, on the freeway,.... and even in the dark!
I figured out why mine doesn't do that. The rubber seal is gone that the tank vent seals against when you close the cap.