2004 SR Johnson 2-stroke 40, 50HP Service Manual, Page 141Get this manual
FUEL SYSTEM OMS PUMP OPERATION
OMS PUMP OPERATION
4050 PL MODELS
The OMS pump uses an air motor powered by crankcase pulses to drive the fuel diaphragm and the oil pistonPump output supplies pressurized fueloil mix to the carburetorsRefer to OMS Pump Diagram on p141
Air Motor Moves to Left
As the pressure in the two chambers of the air motor equalize, the following occurs:
Air Motor
The air motor spring (9) pushes the air motor diaphragm (7) to the left
The fuel diaphragm (12) is pushed into the fuel inlet chamberThe fuel in the chamber passes through the fuel diaphragm's flapper valve into the fuel outlet chamber
Air Motor Moves to Right