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Tohatsu M5B Troubleshooting
The Tohatsu M5B is a two-stroke single-cylinder gasoline outboard engine. This engine has a carburetor fuel system, forced water cooling, and flywheel magneto CDI ignition system. A 6.2 cu.in (102 cc) outboard motor has a cylinder bore of 2.17" (55 mm), piston stroke of 1.69" (43 mm), and maximum power of 5 hp (3.7 kW) at 4500-5500 rpm. The boat motor is equipped with a forward-neutral-reverse gear shift, manual starting system, 3-blades aluminum standard propeller, manual trim and tilt, and tiller handle or remote control steering system. The built-in fuel tank has a capacity of 0.65 gal (2.5 liters).
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| Engine starts hard or will not start |
Gas tank is empty - Fill fuel up.
Low-quality gasoline - Use correct gasoline grade.
Air in fuel system - Bleed fuel system.
Loose or disconnected spark plug wire - Inspect the spark plug wire connection, replace or repair.
Spark plug is faulty - Change spark plug.
Plugged fuel filter - Fuel filter needs changing.
Carburetor is dirty - Wash, clean and adjust.
Fuel lines clogging - Fuel lines must be clean.
Fuel tank air vent restricted or closed - Open or clean air vent.
Low fuel pump pressure - Replace or rebuild fuel pump.
Reed valve is faulty or worn - Install new reed valve.
| Engine starts and stops |
Spark plug is damaged - Spark plug need to be replaced.
Defective or clogged carburetor - Carburetor needs to be replaced or cleaned.
Ignition coil is defective - Install a new ignition coil.
Closed or restricted fuel tank air vent - Open or service air vent.
Low fuel pump pressure - Change or rebuild fuel pump.
| Unstable engine running |
Ignition failure - Check ignition system and replace faulty parts.
Fuel pump is defective or dirty - Clean or change fuel pump.
Carburetor problems - Carburetor diagnostics required.
Dirt in the fuel lines - Clean fuel lines.
Closed or restricted fuel tank air vent - Open or clean air vent.
Fuel filter is plugged - Install new filter.
Gaskets are damaged - Change gaskets.
| Engine overheats |
Engine overloaded - Reduce engine load.
Too lean carburetor mixture - Adjust carburetor properly.
Improper ignition timing - Set the ignition timing correctly.
Defective thermostat - Change thermostat as required.
Damaged water pump - Water pump need to be replaced.
Propeller selection improperly - Replace propeller.
Damaged or bent propeller - Have propeller repaired or replaced.
Outboard engine is mounted too high or too low - Mount the motor as required.
| Engine knocking or noise |
Stale gasoline - Change fuel.
Excessive engine load - Load reducing is recommended.
Incorrectly set low idle speed - Correct the settings.
Dirty or faulty fuel pump - Clean or replace fuel pump.
Main bearings or crankshaft wear - Need to install new components.
Cylinder bore or piston rings are damaged - Replace defective parts.
| Engine loses power |
Incorrectly adjusted or clogged carburetor - Service or properly adjust carburetor.
Fuel pump is dirty or defective - Clean or install new fuel pump.
Ignition system failure - Inspect ignition system and change failed components.
Damaged gaskets - Install new gaskets.
Powerhead parts are faulty - Replace defective parts as required.
Improper propeller diameter or pitch - Check the propeller size.
Damaged or bent propeller - Have propeller repaired or replaced.
Engine mounted at wrong transom height - Adjust the engine to correct transom height.
Incorrect trim angle - Make the correct trim angle adjustment.
| High fuel consumption |
Improper adjustment of carburetor main jet - Adjust the carburetor main jet correctly.
Spark plug is loose or defective - Tighten or change the spark plug.
Piston, sleeve, or rings are damaged - Replace defective parts.
| Strong engine vibration |
Damaged or improper size of propeller - Have propeller repaired or replaced.
Propeller shaft malfunction - Propeller shaft needs to be replaced.
Weeds in the propeller - Remove and clean propeller.
Engine mounting bolt is not tightened - Tighten bolt.
Steering pivot is faulty or loose Tighten correctly or replace.
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