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Tohatsu MFS6CS Troubleshooting
The Tohatsu MFS6CS 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, forward-neutral gear shifting, starting system with recoil starter, flywheel magneto CDI ignition system, manual trim/tilt, and handle tiller or remote control steering. The separate 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 is not starting or hard starting |
Gas tank is empty - Add fuel.
Incorrect fuel grade - Use correct fuel grade.
Air in the fuel system - Air bleeding.
Faulty spark plug wire connection - Check spark plug wiring connection, repair or change.
Faulty spark plug - Replace spark plug.
Fuel filter is dirty - Replace or clean fuel filter.
Problems with carburetor adjustment - Adjust as required.
Fuel lines are dirty - Service fuel lines.
Closed or clogged fuel tank air vent - Fuel tank air vent need to be opened or cleaned.
Defective fuel pump - Replace or repair fuel pump.
Unadjusted or worn throttle cable - Adjust correctly or change the cable.
Valve clearance is not correct - Adjustment procedure required.
Wrong valve timing - Adjust valve timing as required.
| Engine starts but then shuts off |
Defective spark plug - Change spark plug.
Carburetor is clogged or defective - Service or repair carburetor.
Ignition coil is faulty - Change ignition coil as required.
Fuel tank air vent clogged or closed - Open or service air vent.
Faulty fuel pump - Change or rebuild fuel pump.
Choke system is damaged - Inspect and replace choke system components.
Valve clearance is incorrect - Need to adjust valve clearance.
Valve timing is wrong - Adjust valve timing correctly.
Worn or loose valve springs - Install new valve springs.
Valves are stuck - Service the valves.
| Engine runs irregularly |
Ignition system malfunction - Inspect ignition system and change failed components.
Fuel pump is damaged or dirty - Inspect fuel pump and change as required.
Carburetor is dirty - Wash, clean and adjust.
Fuel lines are clogged - Service fuel lines.
Fuel tank air vent restricted or closed - Fuel tank air vent need to be opened or cleaned.
Fuel filter is clogged - Replace or clean fuel filter.
Gaskets are damaged - Change gaskets.
Water intake is clogged - Clean and wash as required.
Choke system malfunction - Inspect and replace choke system components.
| Engine overheats |
Engine is overloaded - Reduce engine load.
Too lean fuel mixture in carburetor - Use proper settings.
Bad ignition timing - Set the ignition timing properly.
Faulty thermostat - Install new thermostat.
Faulty water pump - Change water pump as required.
Propeller pitch or diameter incorrect - Check the propeller size.
Propeller bent or damaged - Have propeller repaired or replaced.
Outboard engine is positioned too low or too high - Mount the motor as required.
Engine oil level low - Fill the crankcase with engine oil.
Oil pump is defective - Oil pump need to be replaced.
Dirty water intake screen - Clean and wash as required.
Improper valve setting - Adjust valves correctly.
| Engine knocks or noises |
Low octane gasoline - Change gasoline.
Excessive engine load - Reduce the load.
Low idle speed setting is incorrect - Correct idle adjustment.
Fuel pump is faulty or clogged - Inspect fuel pump and change as required.
Worn main bearings or crankshaft - Replace crankshaft or bearings.
Damaged piston rings or cylinder bore - Change faulty parts.
| Lack of engine power |
Incorrectly adjusted or clogged carburetor - Clean or properly adjust carburetor.
Clogged or damaged fuel pump - Check fuel pump and replace if necessary.
Ignition system is defective - Test ignition and replace failed parts.
Cylinder head gasket is worn - Cylinder-head gasket replacement required.
Faulty powerhead components - Defective components need to be replaced.
Valves are stuck or burned - Change or clean valves.
Improper propeller diameter or pitch - Replace propeller.
Propeller bent or damaged - Replace propeller.
Motor mounted at incorrect height on transom - Have motor adjusted to proper transom height.
Trim angle is incorrect - Adjust trim angle correctly.
| High fuel consumption |
Carburetor main jet adjustment is incorrect - Adjust the carburetor main jet correctly.
Spark plug is loose or defective - Tighten or replace spark plug.
Worn sleeve, rings, or piston - Change faulty parts.
| Excessive motor vibration |
Propeller bent or damaged - Replace propeller.
Propeller shaft malfunction - Propeller shaft needs to be replaced.
Weeds clogs the propeller - Remove weeds from propeller.
Engine mounting bolt is not tightened - Tighten the bolt as required.
Damaged or loose steering pivot Tighten correctly or replace.
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