1971 Johnson 40HP outboards Service Manual, Page 13Get this manual
TROUBLE CHECK CHART (CONT) TROUBLE POSSIBLE CAUSE ASPARK PLUGSSee Section Cover or inner terminal damaged (spark plug pOint out of H.Tlead) Faulty leads Looselow torque Incorrect heat range Defective (cracked insulator) BMAGNETOSee Section Incorrectly adjusted points Loose wiring Coil or condenser damaged (loose) Fibre breaker block worn Points dirty or pitted Sheared flywheel key 4POOR PERFORMANCE ON BOAT AINCORRECT PROPELLER
3MOTOR MISFIRES (Assuming
Fuel SystemCarburetor OK)
Incorrect tilt angle Incorrect fue mixturetoo much lubricant(smoking) Remote controls incorrectly adj usted Propeller hub slipping Bent or worn propeller Exhaust outlet damaged Bent gear housing or exhaust housing (broken driveshafts) Altitude horsepower loss Catamaran (single engine)venturi effect Exhaust leaks Overheating BCAVITATION Protruding hull attachments Kee too long Bent propeller (vibration) Transom too hi gh CBOAT Improper load distribution Marine growth on bottom Added weight (water absorption) Hook in bottom