Originally Posted by Sohere
I checked and the valve didn't work anymore so I removed it.
If the original tank couldn't get air, because the valve wasn't working anymore, it had to get air from somewhere else.
Can't be the fuel cap cause I swapped this with the one on my brothers f800gs and tank wouldn't get vacuum.
Any ideas where the tank could have
It Can't. That is the only way, unless you have a hole in the tank
. How did you determine that it did not vent. Easy flow towards the tank with the arrow, and need 2-5 psi against the arrow. That is the only way into the tank.