Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 78Get this manual
Testing Fuel Pumps Maximum Fuel Pump Pressure at Wide Open hrottle: 6-8 PSI Minimum Fuel Pump Pressure at Wide Open hrottle: PSI fuel Pressure at Idle PSI Electric Fuel Pump Pressure, if Used Must be Limited to No More than PSI
NOTE: Both eng ine mounted fuel pumps are interchangeableNOTE: Minimum fuel hose inside diameter to engine shou ld be 5 16" (7.9mm) Install clear fuel hose(s) between fuel pump and carburetor(s) Run eng ine, and inspect fuel passing thru hose(s) for air bubblesIf air bubbles are foundsee "Air Bubbles in Fuel Line," belowIf air bubbles are NOT foundseeLack of Fuel Pump Pressu re," below
Troubleshooting Fuel Pump
PROBLEM: Air Bubbles In Fuel Line