I just came across an original 1984 anti siphon valve coming out of my tank doing something similar. These little pumps on the Generators are very poor suckers compared to the diaphragm style pumps the primary engines use so the anti siphon valve being clean and limber is a big deal. They also won't pump air so pull the fuel line off the carb and cap it with your finger to get it to prime as well, not sure why this works but it does. (Thanks to a buddy for all of this info and he was right on)