[JohnB]

anti siphon valve in the gas tank. it is usually located on the end of the pickup tube in the gas tank. With most gas tanks, you can unscrew the fuel tube, and pull it out. If it isn't the filter, it is usually this. You see a lot of these with alcohol gas, as it loosens all the crude in the gas tank, it will plug this. It is a little check valve with a spring. I usually take mine out sinse my gas lines all run above the top of the tank, and won't siphon.