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Tohatsu MFS5C Troubleshooting
The Tohatsu MFS5C is a four-stroke single-cylinder overhead valve shallow water drive gasoline outboard engine. This engine has a carburetor fuel system, mechanical fuel pump, water cooled with thermostat, and flywheel magneto CDI ignition. 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 5 hp (3.7 kW) at 4500-5500 rpm. The boat motor is equipped with a manual starting system, 3-blades aluminum standard propeller, six trim positions, manual tilt, and tiller handle or remote control steering system. The integral fuel tank has a capacity of 0.3 gal (1.15 liters).
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| Engine won't start or hard to start |
No gasoline in tank - Fill it up.
Wrong fuel grade - Use correct gasoline grade.
Air in fuel tank - Bleed fuel tank.
Loose or disconnected spark plug wire - Inspect the spark plug wire connection, replace or repair.
Defective spark plug - Replace spark plug.
Dirty fuel filter - Install new filter.
Carburetor problems - Carburetor diagnostics required.
Dirty fuel lines - Fuel lines must be clean.
Fuel tank air vent restricted or closed - Open or service air vent.
Fuel pump defective - Install new pump or repair it.
Choke cable is unadjusted or damaged - Replace cable or adjust properly.
Excessive valve clearance - Check and adjust.
Incorrect valve timing - Adjust valve timing correctly.
| Engine starts and stops suddenly |
Spark plug is faulty - Change spark plug as required.
Carburetor is faulty or clogged - Clean or change carburetor.
Ignition coil is faulty - Replace ignition coil as necessary.
Closed or clogged fuel tank air vent - Open or clean air vent.
Fuel pump defective - Install new pump or repair it.
Damaged choke system - Change choke system components as required.
Valve clearance is incorrect - Adjustment procedure required.
Wrong valve timing - Set the valve timing properly.
Worn or loose valve springs - Change valve springs.
Stuck valves - Valves must be cleaned.
| Engine runs irregularly |
Defective ignition - Inspect ignition system and change failed components.
Fuel pump is damaged or dirty - Service or change fuel pump.
Problems with carburetor adjustment - Adjust as required.
Dirty fuel lines - Fuel lines need to be cleaned.
Closed or restricted fuel tank air vent - Fuel tank air vent need to be opened or cleaned.
Plugged fuel filter - Change fuel filter.
Gaskets are damaged - Replace gaskets.
Water intake is clogged - Need to clean or wash.
Faulty choke system - Check and repair choke system.
| Engine is overheated |
Engine is under excessive load - Load reducing is recommended.
Carburetor is running lean - Adjust carburetor properly.
Ignition timing is improper - Ignition timing needs to be adjusted correctly.
Damaged thermostat - Thermostat need to be replaced.
Damaged water pump - Change water pump.
Improper propeller diameter or pitch - Replace propeller.
Propeller bent or damaged - Have propeller repaired or replaced.
Outboard motor is mounted too high or too low - Mount the motor as required.
Engine oil insufficient - Check and refill engine oil.
Faulty oil pump - Install new oil pump.
Clogged water intake - Wash or clean as required.
Improper valve setting - Set the valves properly.
| Engine knocking sound or abnormal noise |
Stale fuel - Change gasoline.
Engine is running overloaded - Load reducing is recommended.
Too low idle RPM - Correct idle adjustment.
Clogged or damaged fuel pump - Test fuel pump and replace if necessary.
Main bearings or crankshaft failure - Change or repair worn components.
Damaged cylinder bore or piston rings - Change faulty parts.
| Engine power is insufficient |
Improperly adjusted or dirty carburetor - Adjust the carburetor correctly or clean it.
Dirty or faulty fuel pump - Test fuel pump and replace if necessary.
Ignition failure - Check ignition system and replace faulty parts.
Cylinder head gasket is worn - Cylinder-head gasket replacement required.
Powerhead components are worn - Replace defective components.
Valves are burned or stuck - Service or replace valves.
Propeller selection improperly - Check the propeller size.
Damaged or improper size of propeller - Replace propeller.
Motor mounted at incorrect height on transom - Check the outboard motor mounting height.
Improper trim angle - Make the correct trim angle adjustment.
| Engine uses too much fuel |
Carburetor main jet is incorrectly adjusted - Adjust it properly.
Loose or defective spark plug - Spark plug need to be replaced or tightened.
Sleeve, rings, or piston are damaged - Change defective components.
| Strong engine vibration |
Damaged or bent propeller - Have propeller repaired or replaced.
Propeller shaft damaged - Have propeller shaft replaced.
Weeds in the propeller - Remove weeds from propeller.
Motor mounting bolt is loose - Tighten bolt.
Damaged or loose steering pivot Tighten correctly or replace.
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