Thanks for all of the replies. I think I'll go without the pressurized tank unless it (the engine) wants it.

With a vent line for the tank is there any noticable ether loss for say a 250cc tank (25-30 min run) in your collective experiences? I mean, does the bottom of the tank (last part) make it run a bit hotter/worse, or is this only a factor on really hot days, or never?

Thanks