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Tohatsu MD50B2 Troubleshooting
The Tohatsu MD50B2 is a two-stroke three-cylinder in-line gasoline outboard engine. This engine has a 2-stroke low pressure direct injection fuel system, forced water cooling with thermostat, and inductive ignition system. A 42.5 cu.in (697 cc) outboard motor has a cylinder bore of 2.68" (68 mm), piston stroke of 2.52" (64 mm), and maximum power of 50 hp (36.8 kW) at 5150-5850 rpm. The boat motor is equipped with an electric starting system, 3-blades aluminum standard propeller, manual or power trim and tilt, and tiller handle steering system. The fuel tank has a capacity of 6.6 gal (25 liters).
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| Engine hard to start or will not start |
Fuel tank is empty - Fill gasoline up.
Low-quality gasoline - Use quality gasoline.
Air in the fuel pipes - Bleed the fuel pipes.
Defective wiring connection of spark plug - Check the spark plug wire connection, repair or replace.
Spark plug is damaged - Change spark plug as required.
Clogged fuel filter - Replace fuel filter.
Fuel lines clogging - Clean fuel system lines.
Low fuel pressure - Inspect fuel system for leaks or inspect low pressure fuel pump.
Low air pressure - Check air system components.
Damaged electrical wire harness - Check wiring harness connections.
Ignition system malfunction - Check ignition components and replace if necessary.
Fuel feed pump is not operating - Fuel feed pump need to be replaced.
Fuel injector is clogged or malfunction - Clean or replace as required.
ECM failure - Replace ECM.
Damaged or worn fuel reed valve - Replace reed valve.
| Engine starts but immediately stops |
Spark plug is defective - Install new spark plug.
Defective ignition coil - Ignition coil must be replaced.
Pulse pump is defective - Replace fuel pump.
Fuel system clogging - Clean fuel system.
Fuel filter is plugged - Replace fuel filter.
| Engine runs roughly |
Ignition system failure - Check ignition and replace faulty components.
Spark plug is faulty - Change spark plug as required.
Fuel pump is dirty or defective - Clean or change fuel pump.
Low air pressure - Inspect air system for leaks.
Clogged fuel lines - Fuel lines must be clean.
Dirty fuel filter - Change fuel filter.
Direct injector is defective - Install new injector.
| Engine overheats |
Engine overloaded - Reduce load.
Ignition timing is incorrect - Adjust ignition timing correctly.
Thermostat is faulty - Install new thermostat.
Water pump malfunction - Change water pump.
Propeller selection improperly - Replace propeller.
Propeller bent or damaged - Replace propeller.
Outboard motor is mounted too high or too low - Position the engine correctly.
| Abnormal engine noise or knocking |
Stale gasoline - Use correct gasoline.
Engine is overloaded - Load reducing required.
Wrong adjustment of low idle speed - Correct the settings.
Dirty or defective fuel pump - Check fuel pump and change if required.
Main bearings or crankshaft wear - Crankshaft or bearings need to be replaced.
Worn piston rings or cylinder bore - Replace faulty parts.
| Engine loses power |
Fuel pump is defective or dirty - Service or replace fuel pump.
Ignition failure - Check ignition and replace faulty components.
Worn powerhead components - Replace defective components.
Low fuel pressure - Inspect low pressure fuel pump or inspect fuel system for leaks.
Low air pressure - Normalize air pressure.
Bad compression - Normalize compression.
Fuel delivery problem - Check and repair.
Fuel regulator leaks - Repair leaks.
Dirty fuel filter - Replace fuel filter.
Clogged or worn fuel injector - Clean or replace as required.
Manifold is leaking - Repair leaks.
Propeller selection improperly - Install correct propeller.
Propeller bent or damaged - Have propeller repaired or replaced.
Outboard motor mounting height is set incorrectly - Adjust the engine to correct transom height.
Improper trim angle - Adjust trim angle.
| High fuel consumption |
Spark plug is faulty or loose - Spark plug need to be replaced or tightened.
Sleeve, rings, or piston are damaged - Change defective parts.
Engine overloaded - Reduce the load.
Clogged or damaged fuel injectors - Check fuel injectors and change if required.
| Excessive engine vibration |
Damaged or improper size of propeller - Replace propeller.
Propeller shaft damaged - Have propeller shaft replaced.
Weeds clogs the propeller - Remove and clean propeller.
Engine mounting bolt is not tightened - Tighten the bolt as required.
Steering pivot is faulty or loose - Tighten or replace.
| Starter motor won't turn |
Propeller bent or damaged - Replace propeller.
Propeller shaft damaged - Replace propeller shaft.
Weeds wraped around propeller - Remove weeds from propeller.
Engine mounting bolt is not tightened - Tighten bolt.
| Trim motor runs but trim system does not move up or down |
Low oil level - Fill up oil.
Pump assembly is damaged - Check pump and change if required.
Leakage of manual release valve - Valve need to be closed or changed.
Motor or pump driveshaft faulty - Change worn component.
| Trim cannot be fully up or down |
Pump assembly is defective - Change pump.
Tilt ram piston ball is not positioned correctly - Service or repair.
Damaged tilt ram piston O-ring - Replace O-ring.
Oil insufficient - Fill up oil to required level.
Lower check valve is not properly secured in port side trim ram - Secure valve properly.
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