A Basic Guide to Troubleshooting Common Outboard Motor Problems

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Due to technological advancements, today’s outboard motors are more reliable than ever. Boat enthusiasts around the world continue to choose outboard motors because of the wide variety of benefits they offer:

  • High horsepower to weight ratio
  • Ease of installation and maintenance
  • Extended maintenance intervals
  • Increased use of boat interior space as compared to inboard or sterndrive applications 

However, just like any motor, outboard motors require seasonal and preventative maintenance. As a boat owner or marine technician, it’s important to be aware of these in order to keep your motors in excellent shape and be able to troubleshoot them if a problem occurs.

Keep reading to learn about common boat engine problems as well as some helpful outboard motor troubleshooting tips. 

Common Boat Engine Problems

Outboard motor problems can range anywhere from quick, simple fixes to more complex repairs. In either case, it’s important to spot these problems to be able to diagnose them quickly to avoid a mishap on the water or cause further damage to the boat.

The following are some of the most common issues that can occur in outboard motors.

Fuel-related Issues

Issues related to fuel are some of the most common to occur with outboard motors. The symptoms for fuel-related issues can vary from the engine being hard to start, the engine starting but dying, or the engine starts and runs but will surge or sputter due to the fact that it’s not getting enough fuel.

Fresh, clean fuel is needed for proper operation to take place. If the fuel filter is dirty, this can cause operational problems. Filters are easy to change, and this is a good first step to eliminate a filter as a potential problem.

In many cases, a portable marine fuel tank and hose can be temporarily attached to the engine to eliminate the boat fuel tank and system as the cause of an operational fault. If the engine performs normally when running on the portable fuel tank, you’ve identified the boat’s fuel tank and system as the location of the fault.

Possible causes may include:

  • Water in the boat fuel tank
  • Old, stale fuel in the boat fuel tank
  • Kinked fuel supply hose causing fuel restriction
  • Faulty fuel line connector
  • Faulty primer bulb

Electrical-related Issues

In the case of an engine not starting, there could be a few reasons as to why this is happening. If the boat has been sitting for a while, the engine might turn over but not run or the engine won’t turn over, therefore it won’t run. In order to determine a solution, it’s important to know which situation is occurring.

If you have a fully functioning, charged battery, check to ensure the lanyard is installed. With some manufacturers, the engine won’t turn over without it. Also check to ensure the ship control handle is in neutral, as the neutral safety switch might not be engaged, preventing it from turning over.

Additionally, check for any blown fuses on the engine. If it turns over but won’t start and run, you may not be getting fuel to the engine. Also prime the primer bulb to ensure it’s working properly, and look for loose hose clamps or kinks in fuel lines. If it still doesn’t start, it could be fouled spark plugs or filters that are clogged, and fuel isn’t getting to the engine.

Outboard Ignition Coil Symptoms

When issues arise with the ignition system, there is a chance it’s due to a failed coil. If you have a bad coil, it will impact the cylinder it’s attached to, unless you have a wasted spark ignition, which can affect two cylinders on the engine. This typically results in the engine being hard to start, especially when it’s cold. The boat won’t be able to achieve its maximum RPM due to low power. 

If you have a coil that is damaged but hasn’t completely failed, an engine misfire will occur. This will cause the engine to surge on and off as you’re going through the water. When checking the coil on your outboard, make sure it is free of cracks and is completely intact. If it’s not in good condition, it will need to be replaced. 


Overheating is another problem that can arise with outboard engines. Whenever you start up the engine, look to see if you have a tell tail water stream coming out of the engine overboard water indicator. This is a visual indicator of water pump function. 

If you don’t see any water coming out, it doesn’t necessarily mean it isn’t working. If the boat has been sitting for a little while, it could be clogged with debris or insects. To solve this, take a piece of weed eater string and cut the end at a 45 degree angle. Then, put it in the hole from the outside of the outboard and twist it as you push it through and pull it back out. If water starts to flow, this is your solution. 

It’s important to note the engine speed when overheating begins. Is the boat idle, or at a high RPM? If it’s overheating when idle and the water is flowing, it could be a thermostat issue. If you’re idle and no water is flowing, something could be blocking the water from getting in, which can lead to water pump damage. If the boat overheats at a high speed it could be a pressure control valve, or when there’s not enough water pressure to maintain the cooling of the engine, the water pump needs to be serviced.

Symptoms of Bad Spark Plugs Outboard

Spark plugs are an important element of your boat’s engine. At one end, they take in high voltage electricity and at the other, create a spark. This spark fires the fuel and air mixture in the engine and creates combustion, which your boat relies on for power.

Faulty spark plugs can have the same symptoms as a failed coil. If you have a failed spark plug, this means you’re not burning fuel in the combustion chamber. Therefore, the boat will be low on power, hard to start and may surge or sputter.  

Remove and inspect the spark plugs. If they’re really dark in color and have build-up, there’s a good chance they are fouled and need to be replaced. 

Propeller Issues

It’s common for propellers to get caught up in fishing line, weeds and hit logs or rocks. Depending on the area you’re using your boat in, it’s wise to always do a visual inspection of your propellers and check for cracks, dings, bends and any kind of physical damage. 

If your propeller passes a physical inspection, there may be an underlying issue, such as a spun hub. When this occurs, your boat will likely be able to operate at a lower speed RPM, but will have a hard time accelerating to a higher speed RPM. If this is the case, you will likely want to see a marine mechanic, who can complete the repair for you.

Outboard Motor Not Running at Full Power

If the engine isn’t running at full power, there could be many potential causes. Common causes include spark plugs, dirty fuel filter or water in the fuel.

If investigating any of these factors doesn’t lead to a solution, it’s always wise to consult with a marine mechanic. They are professionally trained to diagnose common outboard motor problems and can determine the repair that is best suited for your boat. 

Engine Vibrating

If you notice that your boat’s engine is vibrating, it could be the spark plugs, fuel filters, propeller, primer bulb, a lack of adequate fuel or worn and damaged engine mounts, which can cause the engine to shake or vibrate. Check each of these elements to see if you can spot any issues. As with any issue you come across in your boat, it’s always beneficial to consult a marine mechanic.

Outboard Motor Troubleshooting

As a marine enthusiast, it’s important to complete a thorough visual inspection on your boat every now and then. Whether your engine runs poorly or you want to check over everything on your boat before spending a long day on the water, here are some steps to follow:

  1. Check the fuel filter: These filters separate out any water that might be present in your fuel, and they also filter out any particulate matter before reaching the engine. When they become filled with water or clogged, it can lead to an engine mishap. Check to ensure that the filter is working properly, and if there are any signs of damage or it is old, go ahead and change it.
  2. Ensure the primer bulb is priming up: Primer bulbs prime the fuel lift pump with fuel. You should be able to prime the primer bulb so it becomes hard, which is a sign that it’s working. Always be sure to check for any leaks or damage.
  3. Check your battery: It’s always wise to check the condition of your battery. This might sound simple, but it’s a critical component of keeping your boat up and running. Check that all connections are tight and free of corrosion. A battery load tester or battery analyzer can be used to check the battery condition (if you suspect the battery is bad, you can usually get it tested at your local auto parts store for free). Most usually, the hydrometer has readings marked that indicate the condition of the battery, making it easy to check.
  4. Analyze the fuel connector: Sometimes, the connectors that attach the fuel line to your outboard become corroded, which can hinder fuel flow. To check your connectors, simply disconnect the fuel line and analyze the outboard end of the connector. Even if the inside passes the test but the outside is worn and corroded, replace it with a new one and reinstall it.
  5. Clean the carburetor: When your carburetor is dirty, this can cause your engine to run poorly. To clean a carburetor, start by using a cleaning spray, which can wash away any debris that might be getting in the way. In most cases, you will have to remove the carburetor in order to fully clean it and then rebuild it. This can be done using a kit or with the help of a marine mechanic.
  6. Check for damaged spark plugs: Damaged spark plugs can lead to a variety of different issues in outboard engines, so it’s important to regularly give them a thorough inspection by pulling each plug to ensure they don’t have any build-up. If necessary, you may need to replace them.
  7. Replace the air filter if necessary: Most outboards don’t use air filters, but there are a few that have them. When air filters get clogged, this can prevent air from getting to the engine, which is necessary for it to run. If your air filter is full of dust and dirt, it’s most likely time to replace it.
  8. Check the fuel line: Fuel lines carry materials from the fuel tank to the engine. If you check your fuel lines and they are starting to deteriorate, crack or split, it’s time to replace them. When replacing fuel lines, always be sure to use marine fuel line instead of automotive fuel line, as automotive fuel line doesn’t meet USCG requirements for marine fuel line.

How This Applies to Your Career

As a marine technician, it’s incredibly important to have knowledge of outboard engines and how they work. This is why UTI’s Marine Technician Specialist Training program, offered at Marine Mechanics Institute (MMI), incorporates these engines into the coursework.

As a student at MMI, you’ll learn everything from the internal workings of the engine itself to electrical systems for ignition, starting, charging and maintenance. You’ll learn about carburetors, electric fuel injection (EFI) systems, basic wiring of a boat as well as have the opportunity to do troubleshooting in class.

In your rigging course, you’ll learn the basics or rigging an engine, trolling motor and installing gauges along with trailer bearings. From there, you’ll have a full 3 weeks of troubleshooting in the electrical diagnostic course. Once you move into your manufacturer courses, you’ll have the opportunity to do troubleshooting on various different manufacturer products.

To learn more about the courses in the marine program, visit our course guide.

According to Billy Crosby, Chief Marine Instructor at MMI-Orlando, “This knowledge is important for students to have because they will be dealing with these kinds of issues on a regular basis. Technicians can encounter these issues on any given day in a marine dealership.” Knowing the ins and outs of these engines can give you a leg up in your career and prepare you for many of the different scenarios you’ll face as a technician.1

Train for a Career in the Marine Industry at MMI

Located in sunny Orlando, Florida, Marine Mechanics Institute offers a 51-week Marine Technician Specialist Training program designed for those looking to turn their passion into a career. To learn more, visit our program page and  request information today. 


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