When a Mercury outboard is hard to start up, it’s a clear sign that something is wrong with the motor. An outboard motor should never require a great deal of effort to activate and begin to work. The motor should turn on effortlessly and without extended cranking.
Sometimes an outboard motor is hard to start but runs fine when started, or is hard starting when the engine is hot or cold, or it’s hard to start after its been sitting for awhile. Whatever the case may be, it’s important to establish the cause of a hard starting engine so as to restore the motor back to working order. Use this troubleshooting guide to get your Mercury outboard to begin operating normally again.
Outboard Hard To Start—Possible Causes And Solutions
- Battery lacking power. Ensure battery is fully charged. Replace battery if it will not hold a charge.
- Battery terminals, cables and connections. Clean battery terminals, tighten connections and look for damaged cables. Test for voltage drop on high amperage circuit.
- Starter or drive gears. Test starter, starter solenoid and its circuitry. Inspect drive gears.
- Water contamination inside fuel system.
- Take a sample of fuel from fuel return manifold test port or fuel filter/water separator.
- Bad or poor quality fuel or fuel contamination. If in doubt, replace fuel. Refer to service manual for fuel specifications.
- Air trapped in fuel system. Check for trapped air in fuel supply system. Refer to service manual for inspection procedures.
- Spark plugs. Check for fouled spark plugs (e.g. broken insulator), correct heat range or for worn plugs.
- Low fuel pressure. Use a fuel pressure tester to check the outboard’s fuel pressure. Refer to factory service manual for testing procedures.
- Low or no alternator output. Check the alternator power output. Check voltage output at circuit. Refer to factory repair manual for testing procedures.
- Circuit wiring or capacitor. Check capacitor and for loose wiring connections. Refer to electrical and ignition analysis in service manual for checking procedures.
- Restricted or leaking fuel injector(s). Check for signs of a leaking fuel injector. Inspect fuel injection wiring. Refer to fuel system check and testing procedures in service manual.
- Fuel supply restricted. Check fuel system for air leaks, check primer bulb, anti-siphon valve and fuel pick-up.
- Erratic or weak ignition timing operation. Check and test ignition timing. Refer to ignition and electrical system analysis in service manual.
- Excessive oil or fuel, engine flooding. Check for signs of a leaking injector, leaking vapor separator vent, or leaking fuel or oil lift pump. Refer to fuel system analysis in service manual.
- Internal engine damage. Inspect and repair as needed. If the engine has compression within factory specifications on all cylinders, yet it’s hard to start and runs poorly, check for damage to powerhead, damage to pistons and or worn or stuck piston rings or the possibilities of scored cylinder walls.
- Leaking crankcase/cylinder, reed valves or intake manifold. Check and repair as needed.
- Crankshaft position sensor CPS. Check and test CPS.
- Faulty enrichment circuit. If the enrichment circuit is defective, while the engine is cold, the motor will be hard to start. Likewise, if the enrichment circuit stays active during normal engine operating temperatures, the mercury outboard engine will flood making it difficult to start the motor.
- Choke stuck in open position. If the choke is stuck open, the engine will be hard to start.
If you have a boat with an outboard motor, and the engine is hard to start, be sure to use these troubleshooting steps to diagnose the problem. It’s also recommended to download the factory service manual. Advance troubleshooting procedures are listed in the book.