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Tohatsu MFS6C Troubleshooting
The Tohatsu MFS6C is a 4-stroke 1-cylinder OHV (overhead valve) gasoline outboard engine with a rated power of 6 hp (4.4 kW) at 5000-6000 rpm. The engine cylinder bore is 2.32" (59 mm) and piston stroke is 1.77" (45 mm). A 7.5 cubic inches (123 cc) outboard motor has a carburetor fuel system, mechanical fuel pump type, wet sump lubtication system, starting system with recoil starter, flywheel magneto capacitor discharge ignition system, manual trim/tilt, and handle tiller or remote control steering. The engine is equipped with a 3.2 gal (12 liters) separate fuel tank or 0.3 gal (1.15 liters) integral fuel tank. The propeller is made of aluminum and it has three blades.
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| Engine starts up hard or will not start |
Gas tank is empty - Fill fuel up.
Improper fuel grade - Change fuel.
Air in the fuel lines - Bleed the fuel lines.
Spark plug wire connection are damaged - Inspect the spark plug wire connection, replace or repair.
Defective spark plug - Install new spark plug.
Clogged fuel filter - Replace or clean fuel filter.
Carburetor settings incorrect - Adjusting as required.
Restricted fuel lines - Service fuel lines.
Fuel tank air vent clogged or closed - Open or service air vent.
Faulty fuel pump - Replace or repair fuel pump.
Choke cable is unadjusted or damaged - Adjust properly or replace the cable.
Excessive valve clearance - Adjust valve clearance according to specifications.
Valve timing is improper - Adjust valve timing correctly.
| Engine stalls after starting |
Spark plug is faulty - Install new spark plug.
Faulty or dirty carburetor - Clean or replace carburetor.
Faulty ignition coil - Ignition coil must be replaced.
Fuel tank air vent closed or restricted - Open or service air vent.
Faulty fuel pump - Replace or rebuild fuel pump.
Choke system malfunction - Check and repair choke system.
Valve clearance is not correct - Adjustment procedure required.
Valve timing is incorrect - Set the valve timing correctly.
Worn or loose valve springs - Replace valve springs.
Stuck valves - Service the valves.
| Engine runs irregularly |
Defective ignition system - Check ignition and replace faulty components.
Fuel pump is defective or dirty - Test fuel pump and change if necessary.
Incorrect carburetor adjustment - Adjust carburetor idle mixture screw.
Fuel lines clogging - Clean fuel lines.
Closed or restricted fuel tank air vent - Open or clean air vent.
Clogged fuel filter - Fuel filter needs changing.
Damaged gaskets - Change gaskets.
Water intake screen is dirty - Wash or clean as required.
Faulty choke system - Check and repair choke system.
| Engine overheats |
Excessive engine load - Reduce engine load.
Carburetor is running lean - Adjust carburetor properly.
Bad ignition timing - Adjust ignition timing correctly.
Defective thermostat - Thermostat need to be replaced.
Water pump failure - Change water pump.
Propeller pitch or diameter incorrect - Replace propeller.
Damaged or improper size of propeller - Have propeller repaired or replaced.
Outboard motor is positioned too low or too high - Mount the motor as required.
Low engine oil level - Check and refill engine oil.
Oil pump malfunction - Change oil pump.
Clogged water intake - Clean and wash as required.
Valve setting is incorrect - Set the valves correctly.
| Engine knocks or noises |
Stale fuel - Use correct fuel.
Engine is overloaded - Reduce engine load.
Improperly adjusted low idle speed - Adjustment required.
Fuel pump is damaged or dirty - Clean or install new fuel pump.
Main bearings or crankshaft wear - Worn parts replacement required.
Cylinder bore or piston rings are worn - Replace defective components.
| Loss of engine power |
Clogged or improperly adjusted carburetor - Service or properly adjust carburetor.
Fuel pump is clogged or faulty - Clean or change fuel pump.
Ignition system problems - Check ignition and replace faulty components.
Blown cylinder head gasket - Install new cylinder head gasket.
Powerhead parts are faulty - Replace defective parts.
Burned or stuck valves - Replace or service valves.
Improper propeller diameter or pitch - Replace propeller.
Propeller bent or damaged - Replace propeller.
Engine mounted at wrong transom height - Check the outboard motor mounting height.
Incorrect trim angle - Adjust trim angle correctly.
| Engine uses too much fuel |
Carburetor main jet is improperly adjusted - Adjust main jet as required.
Loose or faulty spark plug - Tighten or replace spark plug.
Sleeve, piston, or rings are damaged - Change faulty parts.
| Excessive engine vibration |
Damaged or bent propeller - Have propeller repaired or replaced.
Propeller shaft damaged - Replace propeller shaft.
Weeds in the propeller - Clean the propeller.
Motor mounting bolt is loose - Tighten the bolt as required.
Steering pivot is loose or damaged Tighten or replace.
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