________________________________________________________________________________________
| Home / Outboard Engines / Tohatsu Engines / Tohatsu MFS6BS |
Tohatsu MFS6BS Troubleshooting
The Tohatsu MFS6BS 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, water cooling system, starting system with recoil starter, flywheel magneto capacitor discharge ignition, 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.
____________________________________________________________________________________
| Engine doesn't start or difficult to start |
Fuel tank is empty - Fill fuel up.
Wrong grade of gasoline - Change fuel.
Air in fuel system - Bleed fuel system.
Disconnected or loose spark plug wire - Check spark plug wiring connection, repair or change.
Defective spark plug - Spark plug need to be replaced.
Fuel filter is plugged - Replace or clean fuel filter.
Incorrect carburetor adjustment - Adjust carburetor idle mixture screw.
Restricted fuel lines - Fuel lines need to be cleaned.
Closed or clogged fuel tank air vent - Open or clean air vent.
Fuel pump defective - Install new fuel pump or rebuild it.
Worn or unadjusted choke cable - Replace cable or adjust properly.
Valve clearance is incorrect - Adjustment procedure required.
Valve timing is wrong - Adjust valve timing as required.
| Engine starts but stalls suddenly |
Defective spark plug - Install new spark plug.
Clogged or defective carburetor - Service or repair carburetor.
Ignition coil is defective - Change ignition coil as required.
Closed or clogged fuel tank air vent - Open or clean air vent.
Fuel pump malfunction - Replace or repair fuel pump.
Choke system is damaged - Check and repair choke system.
Incorrect valve clearance - Adjust to proper valve clearance.
Incorrect valve timing - Adjust valve timing as required.
Bad or broken valve springs - Change valve springs.
Stuck valves - Service the valves.
| Engine runs intermittently |
Defective ignition system - Check ignition system and replace faulty parts.
Clogged or defective fuel pump - Clean or replace fuel pump.
Incorrect carburetor adjustment - Adjust carburetor idle mixture screw.
Restricted fuel lines - Fuel lines need to be cleaned.
Closed or clogged fuel tank air vent - Open or service air vent.
Fuel filter is plugged - Install new filter.
Gaskets are worn - Install new gaskets.
Water intake screen is dirty - Clean and wash as required.
Damaged choke system - Inspect and replace choke system components.
| Engine overheats |
Excessive engine load - Reduce the load.
Carburetor mixture is too lean - Adjust carburetor properly.
Wrong ignition timing - Set the ignition timing correctly.
Defective thermostat - Replace thermostat.
Water pump failure - Change water pump.
Improper propeller diameter or pitch - Install correct 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 oil level low - Add oil to the engine crankcase.
Oil pump failure - Replace oil pump.
Water intake screen is dirty - Need to wash or clean.
Valve setting is wrong - Valves needs to be adjusted properly.
| Abnormal engine noise or knocking |
Stale fuel - Use proper gasoline.
Engine is overloaded - Load reducing required.
Incorrectly adjusted low idle speed - Test and adjust.
Fuel pump is defective or dirty - Check fuel pump and change if required.
Main bearings or crankshaft wear - Crankshaft or bearings need to be replaced.
Piston rings or cylinder bore are damaged - Change defective components.
| Engine power is insufficient |
Dirty or incorrectly adjusted carburetor - Clean or properly adjust carburetor.
Fuel pump is damaged or dirty - Check fuel pump and change if required.
Defective ignition - Check ignition and replace faulty components.
Damaged cylinder head gasket - Install new head gasket.
Powerhead components are damaged - Change defective parts.
Valves are burned or stuck - Replace or service valves.
Propeller pitch or diameter incorrect - Install correct propeller.
Damaged or improper size of propeller - Have propeller repaired or replaced.
Incorrect outboard motor mounting height - Adjust the engine to correct transom height.
Incorrect trim angle - Make the correct trim angle adjustment.
| Excessive fuel consumption |
Carburetor main jet adjustment is improper - Adjust it properly.
Spark plug is faulty or loose - Spark plug need to be replaced or tightened.
Rings, sleeve, or piston are damaged - Change defective components.
| Engine vibrates excessively |
Damaged or improper size of propeller - Have propeller repaired or replaced.
Damaged propeller shaft - Propeller shaft needs to be replaced.
Weeds in the propeller - Clean the propeller.
Motor mounting bolt is loose - Tighten bolt.
Loose or faulty steering pivot Tighten correctly or replace.
________________________________________________________________________________________
________________________________________________________________________________________
| Engines Technical Specifications |