1980 Johnson 4HP Service Manual, Page 16Get this manual
TROUBLE TROUBLE
CHART (CONT)
POSSIBLE CAUSE POWERHEADSee Section Carburetor and magneto not Throttle control lever won't advance Air leak at manifold gasketswarped manifold {backfires} Broken leaf valves (backfires) Excessive pistons and cyl inder head Stuck piston, rings, scored cyl inder CARBURET ORSee Section fuel mixtoo much lubricont Carburetor adjustments(too leanbackfires) {too richexcessive fuel} Choke not operating properly Air leaks at packing nuts plugs Inlet needle and seat worn sticky Incorrect carburetor float setting Altitude temperature horsepower loss FUEL TANKSee Section Faulty fuel hose clamps seals) Fuel fi ter restricted Shut-off valve not Vent screw not Valves not operoting EXHAUST GAS CARBURETORSee Section Exhaust screws 1eaking plate gasket damaged Exhaust rel ief obstructed Lower motor to exhaust housing gasket leaking Cracked exhaust housing screws loose Exhaust housi ng to lower motor missing OVERHEATING POWERHEADSee Section Lower mator to powerhead gasket improperl insta led damaged Head gasket leaking (warped cylinder head) (water in cylinders) Water ntakes obstructed Pump housing air eed restricted Water passages tube obstructed Pump impeller pl ate worn Pump impell damaged Pump impeller housing cup worn Pump housing seal worn {driveshaft grooved} Water tube improperly installed Pump housi ng grommet 1eaks LOWER UNITSee Section Propel ler hub slipping Bent worn propell Exhaust outlet damaged logged Bent gear housing exhaust housing (broken driveshafts) Bent (vibration)