1985 Mercury Outboard V-300 V-3.4L Shop Service Manual, Page 65Get this manual
Testing Fuel Pumps I nstall clear fu el hose(s) between fu el pu mp and carburetor(s)Run engineand inspect fu el passi ng th ru hose(s) fo air bubblesIf air bubbles are found, seeAir Bubbles in Fuel Line," belowIf air bubbles are NOT found, seeLack of Fuel Pump Pressure," below
Troubleshooting Fuel Pump
POlilble Caul Low fuel in fuel tankLoose lualline connection
PROBLEM' Air BubbleIn Fuel Line Corrective Action
Fill tank with fuelCheck and tighten all connectionsTighten filting Check condition of all fuel lines and replace any found to be badTighten all screws evenly and securely
Fuel pump fitting looseA hole or cut in luailine
Fuel Fuel Fuel Fuel