1972 Johnson 4HP Outboard Motor Service Manual, Page 12Get this manual
TROUBLE
(CONT) CAUSE
2LOSS OF POWER(Assuming (Cont) Ignition
CARBURETORSee Section Poor fueltoo lubricant Carburetor adjustment(too leanbackfires) (too rchexcessive fuel) Choke not operating properly Air leaks at packing nuts or core plugs Inlet needle and seat worn or sticky Boss gasket damaged Incorrect carburetor float setting Incorrect orifice plug FUEL PUMP AND ANKSee Section Faulty fuel hose (poor clamps or seals) (kinked) Fuel tank or filter plugged Fuel filter restricted Fuel and vent valves not opening Valves not operating Operating hose passage restricted Diaphragm leaking or damaged Fuel system hoses plugged ring damaged in connector DGAS ENTERING CARBURETORSee Section Exhaust cover screws leaking Cover plate gasket damaged Exhaust relief obstructed Lower motor cover to exhaust housing gasket leaking Cracked exhaust housing Exhaust housing to lower motor cover screws loose or missing POWER HEADSee Section Lower motor cover to power head gasket improperly installed or damaged Head gasket leaking (warped cylinder head) (water in cylinders) FLOWER UNITSee Section Water intakes obstructed housing air bleed restricted Water passages or tube obstructed plate not sealing (bottom) impeller damaged housing or plate worn housing seal worn (driveshaft grooved) Water tube improperly installed GGASES ENTERING COOLING SYSTEM See Section plate not sealing (bottom) Damaged water tube grommet or ring Pump housing seal damaged (5" adapter seals) Exhaust outlet gasket missing Exhaust housing gasket damaged SPARK PLUGSSee Section Cover or inner terminal damaged (spark plug terminal out of lead) Faulty leads Looselow torque Incorrect heat range Defective (cracked insulator) MAGNETOSee Section Incorrectly adjusted points Loose wiring or condenser damaged (loose) Fibre breaker block worn Points dirty or pitted Defective breaker