Tohatsu MFS4B Troubleshooting
| Engine Model: Tohatsu MFS4B |
| Engine Type: 4-stroke 1-cylinder OHV gasoline outboard engine |
| Total Displacement: 7.5 cu.in (123 cc) |
| Rated Engine Power: 4 Hp (2.9 kW) at 5500 rpm |
| Fuel System: Carburetor |
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| Engine hard starting or not starting |
Empty gas tank - Add gasoline.
Low-quality gasoline - Change fuel.
Air in the fuel pipes - Bleed the fuel pipes.
Loose or disconnected spark plug wire - Check the spark plug wire connection, repair or replace.
Damaged spark plug - Change spark plug as required.
Fuel filter is dirty - Install new filter.
Carburetor is dirty - Wash, clean and adjust.
Restricted fuel lines - Clean fuel lines.
Closed or restricted fuel tank air vent - Open or service air vent.
Fuel pump malfunction - Install new pump or repair it.
Damaged or incorrectly adjusted choke cable - Replace cable or adjust properly.
Valve clearance is incorrect - Adjustment procedure required.
Valve timing is improper - Set the valve timing properly.
| Engine stalls after starting |
Spark plug is faulty - Change spark plug.
Carburetor is faulty or dirty - Repair or clean carburetor.
Ignition coil is not working - Change ignition coil as required.
Closed or restricted fuel tank air vent - Open or service air vent.
Faulty fuel pump - Install new pump or repair it.
Damaged choke system - Change choke system components as required.
Valve clearance is wrong - Check and adjust.
Improper valve timing - Adjust valve timing correctly.
Valve springs are damaged or weak - Install new valve springs.
Valves are stuck - Valves need to be cleaned.
Defective ignition system - Test ignition and replace failed parts.
Fuel pump is defective or dirty - Service or replace fuel pump.
Carburetor is clogged - Clean the carburetor.
Restricted fuel lines - Service fuel lines.
Fuel tank air vent restricted or closed - Fuel tank air vent need to be opened or cleaned.
Dirty fuel filter - Fuel filter needs to be replaced.
Worn gaskets - Install new gaskets.
Water intake is blocked - Need to wash or clean.
Damaged choke system - Change choke system components as required.
Excessive engine load - Reduce load.
Carburetor mixture is too lean - Set the carburetor properly.
Incorrect ignition timing - Ignition timing needs to be adjusted correctly.
Defective thermostat - Change thermostat as required.
Defective water pump - Change water pump as required.
Improper propeller diameter or pitch - Check the propeller size.
Propeller bent or damaged - Have propeller repaired or replaced.
Outboard engine is mounted too high or too low - Position the engine correctly.
Engine oil level is low - Fill up the oil to required level.
Damaged oil pump - Change oil pump.
Clogged water intake - Need to clean or wash.
Incorrect valve setting - Valves needs to be set correctly.
| Engine knocking sound or abnormal noise |
Low octane fuel - Change fuel.
Engine is running overloaded - Load reducing is recommended.
Incorrect low idle setting - Adjust the low idle speed.
Fuel pump is defective or dirty - Service or change fuel pump.
Worn crankshaft or main bearings - Crankshaft or bearings need to be replaced.
Worn cylinder bore or piston rings - Replace faulty components.
| Engine power is insufficient |
Incorrectly adjusted or dirty carburetor - Clean or properly adjust carburetor.
Clogged or defective fuel pump - Clean or change fuel pump.
Ignition system failure - Check ignition system and replace faulty parts.
Cylinder head gasket is blown - Install new head gasket.
Worn powerhead components - Replace defective parts.
Valves are stuck or burned - Clean or replace valves.
Improper propeller diameter or pitch - Check the propeller size.
Damaged or bent propeller - Replace propeller.
Engine mounted at wrong transom height - Check the outboard motor mounting height.
Trim angle is incorrect - Make the correct trim angle adjustment.
| Engine using too much gasoline |
Incorrect adjustment of carburetor main jet - Adjust main jet as required.
Spark plug is faulty or loose - Tighten or replace spark plug.
Rings, sleeve, or piston are damaged - Replace faulty components.
| Excessive engine vibration |
Propeller bent or damaged - Have propeller repaired or replaced.
Damaged propeller shaft - Have propeller shaft replaced.
Weeds wraped around propeller - Remove weeds from propeller.
Motor mounting bolt is loose - Tighten bolt.
Damaged or loose steering pivot Tighten or replace.
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| Outboard Engines Technical Specifications |
| Small Engines Technical Specifications |
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| Industrial Engines Technical Specifications |
