Coast Guard requires an anti siphon valve in line on any fuel tank that drops lower than the outlet on the tank to prevent siphoning of fuel into the bilge in case there is a break in the fuel line. Most outboards have problems with anti siphon valves becasue the fuel pumps create so little vacuum. Old carb I/O and IBs used mechanical fuel pumps that would draw more than enough vacuum to over ride the check valve, newer engines with electric fuel pumps don't pull enough vacuum to over ride the check valve with out casuing issues, so they are now installing electric anti siphon valves that are tied into the fuel line. Most people float test the antispion valves. If you want to stay legal(not that anyone goes poking around in your bilge), install a manual shutoff valve, they meet the requirements for an outboard boat, you don't even have to turn it off, its just here in case you have a broken fuel line
|