I think a lot of folks called that the anti-slosh seal. I've been replacing them in all of the older YFs I rebuild. Originally that seal was to keep gas from sloshing up and out the slot into which the lifter link fits when the vehicle went around a corner or was on a steep hill. The problem we have today is ethanol laced gasoline will "creep" up the float bowl until it reaches that area so we have 2 ways gas can dribble out and down the lifter link. If anyone needs one of these (and the metal retaining piece that was used in conjunction with it), please let me know.
