1978 Johnson 55 HP Outboards Service Manual, Page 35Get this manual
TESTING FUEL PUMP Conduct this test on the motor in test tank or on the boat1
Remove carburetor to fuel pump hoseConnect fuel pressure gauge between the carburetor and fuel pumpNOTE
Before testing, loosen fuel tank gas cap momentarily to release any pressure that may have built upFuel tank must not be more than 24 inches (60 cm) below fuel pump2Start motor and observe gaugePump pressure should read as belowRPM 600 psi (7 kPa) 2500 to 3000 1.5 psi (10 kPa) 4500 2.5 psi (17 kPa)