Outboard motor troubleshooting is the main source of information requests on the outboard motor forum. Outboard motor faults can generally be grouped into the most common areas. In many cases faults and issues can be avoided with good maintenance. Spring brings joy to most boaters but this turns bad when they find that failing to properly winterize and do the boat maintenance comes back to bite them. I suggest you look at the measures outlined in the outboard motor winterizing section, and make sure you have done many of those suggestions. This is a major cause behind many questions asked on the outboard forums by people seeking outboard motor troubleshooting advice.
There are a number of areas that will cause a start failure. There is the fuel system and there is the ignition system.
The first question is whether the fuel is clean and fresh. Many problems happen after winter, and the expectation is that a motor will start and run. Change the fuel and/or remix fuel using new premium grade fuel.
Make sure the fuel tank is clean and the fuel hose and bulb are clean and flushed through as there will be some fuel residues left inside. Check the fuel hose very carefully, and also the bulb. Look for signs of perishing that could cause an air leak. Check the fuel tank cap and ensure the
Make sure there are no kinks in the fuel hose that could cause fuel starvation. Check the engine fuel filter. I think fuel filters should be replaced after every season. They don’t take much sediment and particles to get partially clogged. Check the fuel tank filling cap. They have a one way valve installed that allows air to come in the fuel tank as the fuel gets taken out by the engine. If they are not functioning correctly a vacuum lock can be created that stops air coming in and therefore no fuel is leaving the tank. If the fuel tank cap is suspect then slightly unscrew it to allow air to come in. Run the motor once again and if it then runs as it should then you know the cap needs replacement.
If it is not one of these fundamental reasons then it is time to start looking at engine fuel systems, as old fuel left in the system can cause some gumming up in parts of the system. Fuel pumps can be an issue along with fuel injection or carburettor systems. So many questions on this asked on the forums by people seeking outboard motor troubleshooting advice.
Many rough running situations also involve checking some basics. So many questions asked on the forums by people seeking outboard motor troubleshooting advice. I know quite a lot of people who replace the plugs every season. The spark plug carries the high voltage into the cylinder and ignites the fuel. It is important to clean and check spark plugs regularly. The spark gaps should be measured and adjusted to the correct clearance. The exterior ceramic or porcelain insulation must also be kept clean to prevent tracking to ground and reducing the ignition voltage. Plug lead connections should be checked for corrosion and tightness. The main causes of spark plug problems are incorrectly set gaps or carbon fouling which short circuits the plug to ground. If you run for extended periods at slow outboard speeds, the spark plug electrode erosion will increase, and there will be increased deposits of carbon powder. Once the gap erodes to around 0.040 the motor will start misfiring, idle badly and have trouble starting. The more slow speed running requires regular cleaning and adjustment. If spark plug gaps are too close the reduced spark will not ignite the fuel properly. If it is too large the voltage will not be able to arc across and create the spark that ignites the fuel. Causes of weak spark voltages include a failing magneto coil; clearance problems with magnets on the flywheel; connection problems from the magneto to the coil, or a loose ground connection. The battery charge level does not effect the ignition, if the engine starts then the ignition voltage is being supplied from the magneto.
Plug color is golden or light brown then its good
Plug is damp with fuel, then poor or no ignition or spark plug failure
Plug is dry, then minimal or no fuel
Plug is black and carbonized then the fuel mixture is too rich, or the spark is weak or no ignition, the oil and fuel mixture ratio is incorrect, or as sometimes happens you have installed the wrong plug types
The ignition cables carry the high voltage to the spark plugs. Ignition cables degrade over time, and should be kept clean and dry. When the insulation cracks, tracking and grounding occurs. The rubber boots or covers over the connections should also be clean and seal well. Vibration also causes problems and the cables should be inspected for fatigue and cracking. Rough running is often caused by spark plug cable problems. So many questions asked on the forums by people seeking outboard motor troubleshooting advice. More great outboard boat motors. More great information on fishing and boats.