Vented VS non vented

[rocket rich]

I believe that my 9.8 Tohatsu runs better with the tank fill cap allowing venting?? Any comments?????is this harmfull

 

[Sea Rider]

I would prefer doing same if having same tank, just expect some small fuel spills through cap when boating if tank is fully filled. Assume fuel pump will pump with less effort than if being with cap fully screwed in.

Happy Boating