Mercury Mariner 200, 225 Optimax Outboards Service Manual, 90-855348, Page 132Get this manual
Testing Fuel Pump Install clear fuel hose(s) between fuel pump and carburetor(s)Run engine, and inspect fuel passing thru hose(s) for air bubblesIf air bubbles are found, see "Air Bubbles in Fuel Line," belowIf air bubbles are NOT found, see "Lack of Fuel Pump Pressure," below
Problem: Air Bubbles in Fuel Line
Low fuel in tankLoose fuel line connectionFuel pump fitting looseA hole or cut in fuel lineFuel Pump anchor screw(s) looseFuel Pump filter cover anchor screw looseFuel pump filter gasket worn outFuel pump gasket(s) worn outFill tank with fuelCheck and tighten all connectorsTighten fittingCheck condition of all fuel lines and replace Tighten all screws evenly and securelyTighten screws securelyReplace GasketRebuild fuel pump