Description of Fuel System
1989 Johnson Evinrude Outboards 120/140/200/225/300 HP
The VRO pump is a combination mechanical fuel and oil ~ pump, powered by crankcase pressure and vacuum pulses, which respond to various engine power settings by injecting the proper amount of oil into the fuel system.
The VRO pump incorporates a circuit that warns the operator of a "no oil" situation.
The carburetors meter and distribute the fuel consumed. They control engine speed and power output by varying the intake charge density. To react correctly to a wide range of operating conditions, the carburetors have several discrete fuel mixing circuits.
Carburetor calibration is controlled by an idle air bleed orifice, an intermediate air bleed orifice, and a high speed fuel orifice.
V8 engines are equipped with a fuel manifold bypass valve. Although normally closed, the pressure sensitive bypass valves can react to a reduction in VRO fuel pressure. If one VRO pump output is reduced, the bypass valve will open and allow the other VRO pump to supply fuel and oil to both manifolds.
Under some conditions, one VRO pump might not be capable of maintaining sufficient fuel supply to provide full throttle operation. However, part throttle operation should be available under most conditions.
Mixture enrichment for cold starting is controlled by a fue primer solenoid. When activated at the keyswitch, the solenoid diverts some VRO pump output directly to the intake manifolds.
One OMC Electric Fuel Primer Pump Kit PIN 174651 is supplied with each V8 outboard. When activated with a spring-loaded, momentary switch, the pump fills the fuel distribution lines and engine fuel system for quicker starting. You must not use a fuel primer bulb in a V8 fuel system.-
V4 Comm., V6 and V8 outboards are equipped with a vacuum sensitive switch which sounds a continuous tone of the warning horn if restrictions in the boat fuel supply system reach a critical point.
Updated on: Thursday, August 12, 2021