Mercury Mariner 200, 225 Optimax Outboards Service Manual, 90-855348, Page 187Get this manual
Air Compressor Pressure Test Install Pressure Gauge Assembly 91-852087 to fuel rail pressure test valvesStarboard rail has fuel pressure test valvePort air rail has fuel pressure test valve
NOTE: After 15 seconds of cranking engine with starter motor, air pressure gauge should indicate 80 PSI and fuel pressure gauge should indicate 90 PSI