I posted this on the Cruiser forum and got few answers.
I just bought a Vulcan 900 LT. Yeah, I love it so far. Here is the biggest concern I have - the gas tank.
I fill up the tank, go on a two or three hour ride and go to fill it up again. When I release the tank's cap (requires the key), air rushes INTO the tank and the tank actually expands back to its original size. The first time I saw this I thought, "No way!" Then I saw it again. Other forumites have told me that the tank is pressurized (because of the gasoline sloshing around) and that when I remove the cap and am RELEASING pressure. No way. When I remove the cap, I am releasing a vacuum and the tank expands. I have seen this three separate times and it is the same every time. Suction, tank expands. I have over 800 miles on the bike, so I have put a few gallons into it and I see it over and over again.
Isn't there some venting system built into the cap or the tank to prevent this, or is this normal for the Vulcans? Weird problem, I will admit, but I would like an answer just the same.
Little help, please?