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Tohatsu MFS6B Troubleshooting
The Tohatsu MFS6B is a four-stroke single-cylinder overhead valve gasoline outboard engine. This engine has a carburetor fuel system, mechanical fuel pump type, water cooled with thermostat, and flywheel magneto CDI ignition system. A 7.5 cu.in (123 cc) outboard motor has a cylinder bore of 2.32" (59 mm), piston stroke of 1.77" (45 mm), and maximum power of 6 hp (4.4 kW) at 5000-6000 rpm. The boat motor is equipped with a dog clutch shift system, 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 0.3 gal (1 liters).
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| Engine will not start or starts up hard |
No gasoline in tank - Fill it up.
Improper fuel grade - Use quality fuel.
Water or air in fuel system - Remove air or water from system.
Damaged spark plug wiring connection - Check the spark plug wire connection, repair or replace.
Spark plug is faulty - Install new spark plug.
Plugged fuel filter - Fuel filter needs changing.
Wrong carburetor adjustment - Adjusting carburetor correctly.
Dirty fuel lines - Fuel lines must be clean.
Fuel tank air vent restricted or closed - Fuel tank air vent need to be opened or cleaned.
Faulty fuel pump - Replace or rebuild fuel pump.
Damaged or not adjusted choke cable - Adjust correctly or replace the cable.
Incorrect valve clearance - Check and adjust.
Valve timing is wrong - Adjust valve timing correctly.
| Engine starts and stops |
Spark plug is damaged - Change spark plug as required.
Carburetor is dirty or faulty - Service or repair carburetor.
Ignition coil is faulty - Ignition coil must be replaced.
Fuel tank air vent restricted or closed - Fuel tank air vent need to be opened or cleaned.
Fuel pump is faulty - Repair or change fuel pump.
Choke system malfunction - Change choke system components as required.
Valve clearance is wrong - Adjustment procedure required.
Valve timing is wrong - Adjust valve timing correctly.
Loose or worn valve springs - Install new valve springs.
Stuck valves - Valves must be cleaned.
| Engine runs unevenly |
Ignition failure - Check ignition and replace faulty components.
Fuel pump is clogged or faulty - Test fuel pump and change if necessary.
Carburetor components worn out - Repair or replace parts.
Dirt in the fuel lines - Fuel lines need to be cleaned.
Fuel tank air vent closed or restricted - Open or clean air vent.
Dirty fuel filter - Replace or clean fuel filter.
Gaskets are defective - Install new gaskets.
Clogged water intake - Clean and wash as required.
Damaged choke system - Change choke system components as required.
| Engine overheats |
Engine is running overloaded - Load reducing required.
Carburetor is running lean - Adjust carburetor correctly.
Incorrect ignition timing - Adjust ignition timing correctly.
Damaged thermostat - Install new thermostat.
Water pump failure - Change water pump.
Incorrect propeller selection - Replace propeller.
Damaged or bent propeller - Replace propeller.
Outboard motor is positioned too low or too high - Mount the motor as required.
Engine oil level is low - Check oil level and add oil as required.
Damaged oil pump - Install new oil pump.
Water intake is blocked - Need to wash or clean.
Incorrect valve setting - Valves needs to be set correctly.
| Engine knocking sound or abnormal noise |
Stale or low octane fuel - Change fuel.
Engine is under excessive load - Reduce engine load.
Incorrectly adjusted low idle speed - Correct idle settings.
Fuel pump is defective or dirty - Inspect fuel pump and change as required.
Main bearings or crankshaft wear - Replace crankshaft or bearings.
Piston rings or cylinder bore are damaged - Replace defective components.
| Engine loses power |
Incorrectly adjusted or clogged carburetor - Service or correctly adjust carburetor.
Fuel pump is faulty or clogged - Clean or replace fuel pump.
Ignition system problems - Check ignition and replace faulty components.
Damaged cylinder head gasket - Replace the gasket as required.
Powerhead parts are faulty - Change defective parts.
Burned or stuck valves - Service or replace valves.
Incorrect propeller selection - Replace propeller.
Damaged or bent propeller - Replace propeller.
Outboard engine mounting height improperly - Check the outboard engine mounting height.
Trim angle is incorrect - Adjust trim angle.
| High fuel consumption |
Improper adjustment of carburetor main jet - Adjust the carburetor main jet properly.
Defective or loose spark plug - Tighten or replace spark plug.
Worn piston, rings, or sleeve - Replace faulty components as required.
| Motor vibrates excessively |
Propeller bent or damaged - Replace propeller.
Propeller shaft malfunction - Propeller shaft needs to be replaced.
Weeds in the propeller - Remove weeds from propeller.
Engine mounting bolt is not tightened - Tighten bolt.
Steering pivot is loose or damaged Tighten correctly or replace.
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