Yamaha 25NMH Troubleshooting
| Engine Model: Yamaha 25NMH |
| Engine Type: 2-stroke 2-cylinder gasoline outboard engine |
| Total Displacement: 24.1 cu.in (395 cc) |
| Rated Engine Power: 25 Hp (18.4 kW) at 6000 rpm |
| Fuel System: Carburetor |
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| Engine starts hard or will not start |
Empty gas tank - Fill it up.
Incorrect fuel grade - Use quality gasoline.
There is air in the fuel system - Bleed the system.
Faulty spark plug wire connection - Inspect spark plug wiring connection, change or repair.
Spark plug is defective - Change spark plug.
Clogged fuel filter - Change fuel filter.
Carburetor incorrectly set - Set carb correctly.
Fuel lines are clogged - Fuel lines must be clean.
Fuel tank air vent clogged or closed - Open or clean air vent.
Fuel pump pressure is low - Repair or change fuel pump.
Reed valve is worn or damaged - Replace reed valve.
| Engine starts but then stalls |
Spark plug is defective - Replace spark plug.
Carburetor is clogged or defective - Replace or service carburetor.
Ignition coil is damaged - Replace ignition coil as necessary.
Closed or clogged fuel tank air vent - Open or clean air vent.
Fuel pump pressure is low - Replace or rebuild fuel pump.
Defective ignition - Check ignition and replace faulty components.
Fuel pump is faulty or clogged - Service or change fuel pump.
Carburetor not adjusted - Adjust according to instructions.
Fuel lines are dirty - Fuel lines must be clean.
Fuel tank air vent restricted or closed - Open or clean air vent.
Clogged fuel filter - Install new filter.
Damaged gaskets - Change gaskets.
Engine overloaded - Reduce the load.
Carburetor mixture is too lean - Adjust carburetor properly.
Improper ignition timing - Adjust ignition timing correctly.
Thermostat is defective - Replace thermostat.
Damaged water pump - Change water pump.
Propeller selection improperly - Check the propeller size.
Propeller bent or damaged - Have propeller repaired or replaced.
Outboard motor is positioned too low or too high - Mount the motor as required.
Stale or low octane fuel - Change fuel.
Excessive engine load - Load reducing is recommended.
Incorrectly set low idle speed - Correct the settings.
Clogged or damaged fuel pump - Clean or change fuel pump.
Crankshaft or main bearings wear - Install new parts as as required.
Damaged cylinder bore or piston rings - Change faulty parts.
Carburetor is incorrectly adjusted or dirty - Clean or correctly adjust carburetor.
Fuel pump is defective or dirty - Check fuel pump and replace if necessary.
Ignition system problems - Inspect ignition system and change failed components.
Worn gaskets - Install new gaskets.
Worn powerhead components - Replace defective components as required.
Propeller selection improperly - Check the propeller size.
Damaged or bent propeller - Replace propeller.
Outboard motor mounting height is set incorrectly - Adjust the outboard motor height correctly.
Improper trim angle - Adjust trim angle correctly.
Carburetor main jet adjustment is improper - Adjust it correctly.
Faulty or loose spark plug - Replace or tighten spark plug.
Worn sleeve, rings, or piston - Replace defective components as required.
| Excessive motor vibration |
Damaged or bent propeller - Replace propeller.
Damaged propeller shaft - Replace propeller shaft.
Weeds clogs the propeller - Remove and clean propeller.
Motor mounting bolt is loose - Tighten the bolt as required.
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 |
