Sitting on the deck with a clear bottle and hose, the fuel path becomes visible as the engine runs. Instead of guessing usage, you can literally watch gasoline being drawn into the system second by second. Four stroke outboards use a mechanical or diaphragm fuel pump to pull fuel from the tank and send it into the combustion chamber. As engine speed increases, that demand rises, which is why the flow through the hose becomes more aggressive under throttle. What seems like a small, steady stream