Home / Outboard Engines / Mercury Engines / Mercury 150

Mercury 150 Troubleshooting

Engine Model: Mercury 150 Hp
Engine Type: 2-cycle 6-cylinder gasoline outboard engine
Total Displacement: 121.9 (1998 cc)
Rated Engine Power: 150 Hp (111.8 kW) at 5500 rpm
Fuel System: Carburetor with adjustable jet


Engine will not start or hard to start

Empty fuel tank - Add gasoline.
Wrong grade of gasoline - Use quality gasoline.
Clogged fuel system - Remove clogging.
Defective spark plug wire connection - Check the spark plug wire connection, repair or replace.
Damaged spark plug - Spark plug need to be replaced.
Clogged fuel filter - Replace fuel filter.
Carburetor malfunction - Check and repair as required.
Fuel lines are clogged - Fuel lines need to be cleaned.
Fuel tank air vent clogged or closed - Fuel tank air vent need to be opened or cleaned.
Lack of fuel pump pressure - Repair or change fuel pump.

Engine starts but then shuts off

Damaged spark plug - Change spark plug.
Carburetor is defective or dirty - Replace or service carburetor.
Defective ignition coil - Replace ignition coil as necessary.
Fuel tank air vent restricted or closed - Open or clean air vent.
Fuel pump pressure is low - Replace or rebuild fuel pump.
Faulty thermal relief valve - Replace if necessary.

Engine runs irregularly

Defective ignition - Test ignition and replace failed parts.
Dirty or defective fuel pump - Clean or replace fuel pump.
Carburetor not adjusted - Adjust according to instructions.
Clogged fuel lines - Service fuel lines.
Fuel tank air vent clogged or closed - Open or clean air vent.
Dirty fuel filter - Fuel filter needs changing.
Gaskets are worn - Change gaskets.

Engine overheated

Engine is under excessive load - Reduce the load.
Carburetor fuel mixture is too lean - Adjust carburetor properly.
Ignition timing is improper - Adjust ignition timing as required.
Faulty thermostat - Install new thermostat.
Water pump failure - Change water pump.

Engine noise or knocking

Stale gasoline - Change fuel.
Excessive engine load - Load reducing required.
Incorrect low idle setting - Adjust as required.
Dirty or faulty fuel pump - Test fuel pump and change if necessary.
Worn main bearings or crankshaft - Crankshaft or bearings need to be replaced.
Worn cylinder bore or piston rings - Replace faulty parts.

Engine power is too low

Carburetor is incorrectly adjusted or dirty - Service or properly adjust carburetor.
Clogged or defective fuel pump - Clean or install new fuel pump.
Ignition system malfunction - Inspect ignition system and change failed components.
Gaskets are defective - Install new gaskets.
Worn powerhead parts - Replace defective components.

Excessive fuel consumption

Incorrect adjustment of carburetor main jet - Adjust it properly.
Loose or defective spark plug - Re-tighten or change the spark plug.
Worn piston, rings, or sleeve - Change faulty parts.

Trim motor is running but system can't move

Oil level low - Check and refill oil.
Defective pump assembly - Check pump and change if required.
Manual release valve leaking - Close the valve fully or replace it.
Pump driveshaft or motor damaged - Change defective component.

Trim cannot be fully up or down

Pump assembly is faulty - Change pump.
Tilt ram piston ball is in wrong position - Clean or repair.
Tilt ram piston O-ring damaged - Replace O-ring.
Insufficient oil - Checking oil level and add if necessary.
Lower check valve is not properly secured in port side trim ram - Secure valve properly.