Are These Fuel Sys Pressurized

[VmaXXX]

First fill up following the L3K tank install. Got quite a poof when I popped the gas cap. Never noticed that before. Just wondering if these fuel tanks are supposed to be vented into the atmosphere or are they under pressure.

 

[VmaXXX]

Disregard. A buddy ditched his rollover valve for a long hose that runs uninterrupted from the vent tube and terminates under the swingarm. His machine runs great and the interior of his tank is obviously equal to atmospheric pressure.