1971 Johnson 40HP outboards Service Manual, Page 12Get this manual
TROUBLE CHECK CHART (CONT) TROUBLE POSSIBLE CAUSE APOWER HEADSee Section Carburetor and magneto not synchronized Throttle control lever bent (won't advance) Air leak at manifold gasketswarped manifold (backfires) Broken leaf valves (backfires) Cracked carbon seal (water in cylinders) Excessive carbon on pistons and cylinder head Stuck piston rings, or scored cylinder or .piston Drain leaf holes restricted Leaf stops closed should be open .040 (plug fouling) BCARBURETORSee Section Poor fuel mixtoo much lubricant Carburetor adjustment(too leanbackfires) (too richexcessive fuel) Linkage screws loose Choke not operating Air leaks at packing nuts Inlet needle and seat worn or sticky Incorrect carburetor float setting Boss gasket leaking CFUEL PUMP AND TANKSee Section Faulty fuel hose (clamps or seals) (kinked) Fuel tank or pump filter plugged Fuel filter restricted Fuel and vent valves not opening Valves not operating Diaphragm leaking or damaged Fuel system hoses plugged "0" ring damaged in fuel line connector DEXHAUST GAS ENTERING CARBURETORSee Section Exhaust cover screws leaking Cover plate gasket damaged Damaged exhaust housing seal Adapter gaskets leaking Cracked exhaust housing Exhaust tube to cylinder screws loose or missing EOVERHEATING POWER HEADSee Section Exhaust cover gasket leaking Inner exhaust cover leaking Power head gasket improperly installed or damaged Head gasket leaking (warped head) (water in cylinders) FLOWER UNITSee Section Water intakes obstructed Pump housing air bleed restricted Water passages obstructed Pump plate not sealing (bottom) Pump impeller damaged Pump housing or plate worn Pump housing seal worn (driveshaft grooved) Water tube grommet damaged GEXHAUST GASES ENTERING COOLING SYSTEMSee Section Pump impeller plate not sealing (bottom) Damaged water tube grommets or "0" rings Pump housing seal damaged (5" adapter seals) Exhaust tube to plate gasket damaged