Yamaha 25BMH Troubleshooting
| Engine Model: Yamaha 25BMH |
| Engine Type: 2-stroke 2-cylinder gasoline outboard engine |
| Total Displacement: 30.2 cu.in (496 cc) |
| Rated Engine Power: 25 Hp (18.4 kW) at 5500 rpm |
| Fuel System: Carburetor |
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| Engine hard starting or not starting |
Empty gas tank - Add gasoline.
Improper fuel grade - Use quality gasoline.
Air in the fuel system - Air bleeding.
Defective wiring connection of spark plug - Inspect spark plug wiring connection, change or repair.
Defective spark plug - Install new spark plug.
Plugged fuel filter - Replace or clean fuel filter.
Carburetor incorrectly set - Set carb correctly.
Fuel lines are dirty - Clean fuel system lines.
Closed or restricted fuel tank air vent - Open or clean air vent.
Fuel pump pressure is low - Install new fuel pump or rebuild it.
Damaged or worn fuel reed valve - Install new reed valve.
| Engine starts but stops suddenly |
Spark plug is defective - Change spark plug as required.
Clogged or faulty carburetor - Clean or change carburetor.
Ignition coil is defective - Install a new ignition coil.
Fuel tank air vent closed or restricted - Open or clean air vent.
Fuel pump pressure is low - Replace or repair fuel pump.
Ignition system malfunction - Test ignition and replace failed parts.
Dirty or defective fuel pump - Clean or change fuel pump.
Carburetor incorrectly set - Set carb correctly.
Fuel lines are clogged - Service fuel lines.
Closed or restricted fuel tank air vent - Fuel tank air vent need to be opened or cleaned.
Fuel filter is plugged - Replace or clean fuel filter.
Gaskets are defective - Change gaskets.
Engine overloaded - Reduce load.
Carburetor is running lean - Adjust carburetor properly.
Ignition timing is wrong - Set the ignition timing properly.
Damaged thermostat - Change thermostat as required.
Damaged water pump - Install new water pump.
Incorrect propeller selection - 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.
| Abnormal engine knocking or noise |
Low octane gasoline - Use correct gasoline.
Excessive engine load - Reduce load.
Incorrectly set low idle speed - Correct idle adjustment.
Dirty or faulty fuel pump - Clean or change fuel pump.
Worn crankshaft or main bearings - Have bearings or crankshaft replaced.
Piston rings or cylinder bore are damaged - Replace faulty parts.
| Engine power is insufficient |
Carburetor is incorrectly adjusted or clogged - Carburetor needs to be adjusted correctly or cleaned.
Dirty or faulty fuel pump - Service or change fuel pump.
Defective ignition system - Test ignition and replace failed parts.
Gaskets are worn - Replace gaskets.
Powerhead parts are worn out - Defective parts need to be replaced.
Propeller pitch or diameter incorrect - Install correct propeller.
Propeller bent or damaged - Have propeller repaired or replaced.
Outboard engine mounting height improperly - Check the outboard motor mounting height.
Improper trim angle - Make the correct trim angle adjustment.
| Excessive fuel consumption |
Incorrect adjustment of carburetor main jet - Adjust it properly.
Spark plug is loose or faulty - Re-tighten or replace spark plug.
Piston, sleeve, or rings are damaged - Change defective components.
| Excessive engine vibration |
Damaged or bent propeller - Replace propeller.
Damaged propeller shaft - Replace propeller shaft.
Weeds clogs the propeller - Remove and clean propeller.
Engine mounting bolt is not tightened - Tighten bolt.
Damaged or loose steering pivot Tighten or replace.
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| Outboard Engines Technical Specifications |
| Small Engines Technical Specifications |
| Car Engines Technical Specifications |
| Industrial Engines Technical Specifications |
