Mercury Mariner 200, 225 Optimax Outboards Service Manual, 90-855348, Page 170Get this manual
Fuel Pressure Regulator Regulator Closed Regulator Open
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1Top CoverExpansion PlugO-ringSpring RetainerSpringO-ringDiaphragm SeatAir RailAir Passage (from Air Compressor) 10- Fuel Return Passage (to Vapor Separator) 11- Fuel Inlet Passage (from Electric Fuel Pump) 12- Diagram Assembly 13- Calibration Screw (Do Not Turn)
The fuel regulator is mounted on the port fuel railnear the topThis regulator relies on both air and spring pressure to control the fuel pressureInside the regulator assembly is 10 lbspring, this spring holds the diaphragm against the diaphragm seatThe contact between the diaphragm and diaphragm seat closes the passage between the incoming fuel (from the electric fuel pump) and the fuel return passageWhen the engine is not running (no air pressure on the spring side of the diaphragm) the fuel pressure required to move the diaphragm is 10 psiWhen the engine is running, air pressure from the air compressor (80 psi) is routed through the air passages, to the spring side of the fuel pressure regulator diaphragmThe air pressure (80 psi) and spring pressure (10 psi) combine to regulate system fuel pressure to 90 psi or 10 psi higher than the air pressure in the OFI system fuelair rails