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Tohatsu M8B Troubleshooting
The Tohatsu M8B is a 2-stroke 2-cylinder forced water-cooled gasoline outboard engine with a rated power of 8 hp (5.9 kW) at 4500-5500 rpm. The engine cylinder bore is 1.97" (50 mm) and piston stroke is 1.69" (43 mm). A 10.3 cubic inches (169 cc) outboard motor has a carburetor fuel system, starting system with manual starter, flywheel magneto capacitor discharge ignition system, dog clutch shift system, manual trim/tilt, and handle tiller or remote control steering. The fuel tank capacity is 3.2 gal (12 liters). The propeller is made of aluminum and it has three blades.
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| Engine starts hard or will not start |
Empty gas tank - Add fuel.
Incorrect fuel grade - Change fuel.
Air in the fuel system - Air bleeding.
Defective wiring connection of spark plug - Check spark plug wiring connection, repair or change.
Spark plug is faulty - Change spark plug.
Fuel filter is dirty - Change fuel filter.
Carburetor is not working properly - Inspect and adjust.
Fuel lines are clogged - Fuel lines need to be cleaned.
Closed or restricted fuel tank air vent - Open or service air vent.
Fuel pump pressure is low - Replace or rebuild fuel pump.
Worn or defective reed valve - Replace reed valve as required.
| Engine starts but immediately stops |
Spark plug is damaged - Change spark plug as required.
Defective or clogged carburetor - Clean or replace carburetor.
Defective ignition coil - Ignition coil must be replaced.
Fuel tank air vent closed or restricted - Open or service air vent.
Lack of fuel pump pressure - Install new pump or repair it.
| Engine runs roughly |
Defective ignition system - Inspect ignition system and change faulty parts.
Fuel pump is dirty or defective - Clean or change fuel pump.
Carburetor is clogged - Clean the carburetor.
Fuel lines clogging - Clean fuel system lines.
Fuel tank air vent closed or restricted - Open or service air vent.
Dirty fuel filter - Replace or clean fuel filter.
Gaskets are damaged - Replace gaskets.
| Engine overheated |
Engine is running overloaded - Load reducing required.
Carburetor fuel mixture is too lean - Make the correct settings.
Ignition timing is improper - Ignition timing needs to be adjusted correctly.
Defective thermostat - Replace thermostat.
Damaged water pump - Replace water pump.
Improper propeller diameter or pitch - Install correct propeller.
Propeller bent or damaged - Have propeller repaired or replaced.
Outboard motor is mounted too high or too low - Mount the motor as required.
| Abnormal engine knocking or noise |
Low octane gasoline - Change gasoline.
Engine overloaded - Load reducing is recommended.
Low idle speed setting is not correct - Adjust as required.
Dirty or defective fuel pump - Clean or replace fuel pump.
Crankshaft or main bearings are worn out - Need to install new components.
Cylinder bore or piston rings are worn - Change defective parts.
| Engine power is insufficient |
Improperly or clogged carburetor - Carburetor needs to be adjusted correctly or cleaned.
Fuel pump is defective or dirty - Inspect fuel pump and change as required.
Ignition system malfunction - Check ignition and replace faulty components.
Damaged gaskets - Install new gaskets.
Worn powerhead components - Replace defective parts.
Propeller pitch or diameter incorrect - Install correct propeller.
Propeller bent or damaged - Have propeller repaired or replaced.
Outboard engine mounting height improperly - Have motor adjusted to proper transom height.
Improper trim angle - Make the correct trim angle adjustment.
| Excessive fuel consumption |
Carburetor main jet is incorrectly adjusted - Adjust it properly.
Loose or faulty spark plug - Re-tighten or replace spark plug.
Worn piston, rings, or sleeve - Replace defective parts.
| Strong engine vibration |
Propeller bent or damaged - Have propeller repaired or replaced.
Propeller shaft malfunction - Propeller shaft needs to be replaced.
Weeds clogs the propeller - Remove weeds from propeller.
Motor mounting bolt is loose - Tighten the bolt as required.
Steering pivot is faulty or loose Tighten or replace.
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