I bought this from the states, fitted it (1/2 hour) ,now when the tank is nearly full, there are all sorts of hissing sounds until you brim the tank ,(if you so wish) however there is no wearing a ltr of unleaded as before.
This can be a problem with most boats, if there is room, you could place a small chamber/tank between the main tank and filler to allow for expansion, from the pipe, to stop the fuel from backing up in surges as you get to nearing full, also it helps, when the boat is rocked whilst filling by a passing boat.
