The air motor converts pressure and vacuum pulses from the crankcase into mechanical motion to drive the fuel and oil pumps. The sending unit for the " No Oil" warning The Fuel/Oil Pump is Divided into Four Sections: Later versions added oil at a constant ratio and were called OMS pumps, for Oil Metering System. The pump injects oil into the fuel and pumps the mixture to the carburetors.Įarly versions were called VRO, for Variable Ratio Oiling, because they varied the oil ratio depending on engine speed and load. The pump draws oil from an oil reservoir - mounted inside the boat - and fuel from the fuel tank. Most 40hp and larger, carbureted two-stroke outboards use a combination fuel/oil pump mounted on the engine. The four-stroke fuel pump works in a similar way, except the diaphragm is moved mechanically by a lobe on the camshaft or crankshaft. On two-stroke models, pressure and vacuum pulses from the outboard´s crankcase drives the fuel pump. This pushes fuel past another check valve and towards another carburetor, or fuel injection system. When the piston moves down in the cylinder, pressure rises in the crankcase and moves the diaphragm in the opposite direction. When the pump´s diaphragm movest toward the vacuum.Ītmospheric pressure pushes fuel past a check valve into the pump. The fuel pump is connected to the crankcase by a short hose or a passage between the fuel pump and the crankcase.Īs the outboard's piston moves up in the cylinder, it creates a low-pressure area (vacuum or partial vacuum) in the crankcase. It draws fuel from the boat´s fuel system and delivers it to the carburetor or fuel injection system. Stiff, cracked, worn, and damaged hoses must be replaced.Ī diaphragm-type fuel pump is mounted on the outboard´s powerhead. Fuel flow will be restricted if the valve doesn´t open completely.Īlways inspect all hoses and connectors. Some smaller outboards use "dripless" fuel line connectors, it has a valve that opens when the hose connector is attached. If the o-ring is cracked or worn, fuel can leak from the connector or air can enter the fuel system. The hose end of a "quick disconnect" connector includes an o-ring. Many outboards have a quick-disconnect feature that allows the fuel line to be seperated from the motor. If the hose is connected to anything other than a splash well fitting or a portable tank, it is considered part of the boat´s fuel system and Coast Guard regulations must be followed. Outboard fuel line may be used to connect to a metal thru-hull fitting in the splash well or to a portable fuel tank. The outboard´s fuel system begins with the fuel line, a hose that connects the outboard to the boat´s fuel system.
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