Motorcycle Repair: sunken gas tank, yamaha v star 650, vent tube

Question
Wayne, I would like your help with this problem. I have a 2002 Yamaha v-star 650 classic. The fuel cap fell apart one afternoon and half of it fell into the tank. i put an oil cap in its place but on day the top of the tank sunk in like someone punched it. I popped the dent out using an air compressor and bought a new fuel cap. Well the cap was $90 and the tank caved in again.Is it possible that the is not venting or more likely that I need to remove the tank and search out clogged vacuum lines. Thank you, bill

Answer
Bill,
you definitely have some serious vacuum there.
Tanks often have a vent tube somewhere,it should
connect to your emissions canister.
I would suspect something has plugged it up.
As you drive and the gas goes down, the tank
needs to get air in to replace it.
Without a vent the vacuum created just sucks
the tank inward. It can also restrict your
gas flow, and cause the engine to stall.