1971 Johnson 125HP outboards Service Manual, Page 16Get this manual
2-9 TROUBLE CHECK CHART (CONT) TROUBLE 4ENGINE MISFIRES (Assuming Fuel System and Carburetor OK) (Cont) BPOSSIBLE CAUSE Faulty leads Loose spark plugs (low torque) Defective spark plugs cracked insulator) Incorrect spark plugs DISTRIBUTORSee Section Distributor assembly dirty inside adjusted sensor gap Incorrect timing Loose wiring Rotor pin missing Loose sensor Loose distributor base retainers Coil or pulse pack CORRODED OR CRACKED DISTRIBUTOR CAPROTORSee Section Rotor wave washer missing Loose distributor ground wire Carbon path in distributor cap or rotor Loose or shorted sensor leads INCORRECT PROPELLER Incorrect tilt angle Poor fuel mixtoo much lubricant (smoking) Remote controls incorrectly adjusted Propeller hub slipping Bent or worn propellercoverging ring missing Bent gear housing or exhaust housing Prop shaft bearing housing improperly installed Altitude horsepower loss Catamaran (single engine)venturi effect Exhaust leaks Overheating CAVITATION Protruding hull attachments Keel too long Bent propeller (vibration) Transom too high BOAT Mounts loose loss of rubber bond Improper load distribution Marine growth on bottom Added weight (water absorption) Hook in bottom