Fuel Delivery in 88 90hp Yamaha

[timo14]

My buddy's yamaha is conking out after running for a while. It seems like a fuel delivery problem. The fuel line & vent lines are clear, no clogs. Is there a valve in the fuel tank between the intake tube and the rubber hose? I tried to blow some air into the tank, but i couldn't. I could suck some fuel from the tank though. Thanks

[rodbolt]

most built in tanks have an anti-siphon valve. looks almost like a hose nipple mounted at the fuel draw tube. its a coast gaurd requirement if any part of the fuel system falls below the top of the tank. if it does not fall below the top of the tank I dont think its required now. if ya pump the primer bulb while its dying will it keep going ? sometimes the fuel pumps just get weak.