1974 Johnson 40 HP Outboard Motors Service manual, Page 15Get this manual
TROUBLE CHECK CHART (CONT) TROUBLE POSSIBLE CAUSE
3MOTOR MISF IRES (Assuming
Fuel SystemCarburetor OK)
ASPARK PLUGSSee Section 4
4POOR PERFORMANCE ON BOAT
BCover or inner terminal damaged (spark plug point out oC H.Tlead) Faulty leads Looselow torque Incorrect heat range Defective (cracked insulator) LOW TENSION IGNITIONSee Section Incorrectly adjusted points Loose wiring Coil leads loose Condenser damaged (loose) Fibr breaker block worn oints dirty or pitted Sheared nywheel key inkage improperl adjus ted Driver coil leads loose INCORRECT ROPELLER rn.correct tilt angle Incorrect fu el mixturptoo much lubricant(smOking) Remote contro ls incorre ctly adjusted Propelle hub slipping Bent worn prope lle Exhaust outlet damaged Bent gear hous ing or exhaust housing Altitude hor sepowe los Catamaran (s ing le ng ine)venturi effect Exhaust leaks Overheating CAVITATION Protruding hull attachments Keel too long Bent prope ller (vibration) Transom too hi gh BOAT Imprope load distribution Marine growth on botto Added weight (wate absorption) Hook in bottom