Gas tank building pressure?

[Graveyard]

Doubt it has anything to do with ethanol but bottom line you have pressure buildup that is not being allowed to escape so i would start with blowing out the vent lines with compressed air like Zues said. If those are both clear i would focus on your gas cap its giong to be one or the other or possibly your vent hose is pinched by the engine somewhere and not letting the vapor escape. i know the vortex caps have a very small ball and spring in there to let the vapor escape maybe your spring is shot and sticking i think i have a spair spring and ball if you need i'll just ship to you, let us know what you find.

You and and Jesse gonna make it to NLB again in Nov, Never got a chance to BS with you last time!