Unsure of what type fuel valve you have but will assume it's the one that mounts to outside of cowl and has 2 nipples inside and a nipple that will plug into outside of valve that fuel will feed from to fill tank. Just put a piece of fuel line on the outside nipple then blow through it and check where the air comes out of one of inside nipples. That will be the nipple that goes directly to tank the other goes to motor. You must remove the outside nipple for fuel to flow from tank to motor.