1978 Johnson 4HP outboards Service Manual, Page 28Get this manual
FUEL PUMP AND FILTER Before replacing fuel pump, remove and install new filter screen and gasketSee Figure 3-18Also remove the fuel line from the fuel tank and blow through all passages and lines with compressed air to be sure they are openThis may be the cause of inadequate fuel delivery, and if so, would eliminate unnecessary replacement of the fuel pumpIf this procedure does not correct the trouble fuel pump is probably malfunctioning and should be replaced 600 PSI (7 kPa)
RPM 2500 to 3000 1.5 PSI (10 kPa) 4500 2.5 PSI (17 kPa)
REMOVAL OF FUEL PUMP AND FILTER
Disconnect fuel lines from pump and filter assemblyaTo assure correct reassembly, identify fuel lines before disconnecting bTo remove fuel filter, remove screw and cover attaching filter to fuel pumpSee Figure 3-18cTo remove fuel pump, remove two screws attaching pump to powerhead, and remove pump assemblySee Figure 3-18
CLEANING, INSPECTION AND REPAIR
123456Pump Fuel pump attaching screws Filter cover and screw Gasket Screen Fuel hoses aThe fuel pump operating components are not serviced separatelyIf malfunction occurs, replace the complete pumpbClean all parts of the filter assembly and fuel connectors in solvent and blow dryDO NOT dry parts with cloth, as lint may stick to the parts and clog the passages or prevent the valves from seatingDissolve any gummy deposits with OMC Accessory Engine Cleaner (certain solvents will not dissolve these deposits)