What is connected to the cylinders of an outboard near the spark plugs?

ok so i was running my motor yesterday to check my water pump which i now know is junk and needs replacement. However as i ran it at idle i head a pop noise almost, and later on checked the engine and saw that a line going from the top, through the middle and bottom carbs and then goes to the back of the motor where it plugs into a gold nut near the spark plugs. the piece that broke was a plastic looking piece that is connected to the hose from the carbs, and when it broke i found a spring and a plastic piece that goes inside of the spring. The plastic piece that held the spring ect, snapped where it connects to the gold nut. If anyone knows what this might be please help! ive done a little research and all i can think is possibly a vacuum valve or a retainer of some sort?