[Ross F-1]

Does your tank have a right-angle shutoff valve on the fuel connection? That is what is stock. On its inlet (part that screws into tank) there is a metal tube made out of brass screen that sticks up into the tank. You can't replace it without draining the whole tank.

You should be able to look down thru the filler and see if there is a bunch of crud in the bottom of the tank.