[Roadsters] "sealed" fuel system questions

[Tim]

More questions from the clueless in WI:

What exactly is that little "valve" for right behind the rear carb on my 70 1600 & 2000? How does it work?

Can I remove the this valve, the fuel vapor return line and the trunk tank and not affect how the engine runs?

How important is it to have the gas cap seal correctly on these sealed systems?

Thanks

Tim
Dairyland Datsuns