expansion tank/resovoir for non vented tank

[JohnEd]

Friends,

Hope you indulge gasoline questions.  I have two tanks on an old Windy Bago that won't die proper and I keep for short brief trips.  Problem was always that the vented tanks spewed gas in a left hand turn and rusted when it set awhile.  It sat for a few years and the problem is at a head.  I have an idea of what I want to do an where to place the expansion tank but I am still stupid about some detailes.  How big a expansion tank do I need for 90 gallons of gas.  I plan this to be a "no pressure system with the expansion tank having a vent to alow it to fill and discharge.  Do I have any problems lurking?

Thanks fo giving this a thought.  I expect to keep my gas generator for the bus anyway so the info is staying in the family.

John