1972 Johnson 50 hp...was fishing saturday, headed back to the ramp and motor started bogging down and then quit. looked at the fuel line back there and noticed the fuel bulb coming out of tank was completely sucked in? Never seen that before. I disconnected line from tank an motor and then poked the little ball inside one of the connectors and the ball relaxed...it did it one more time on me after we went to a different lake for some more fishing. What is causing this?