Outboard Motor Won't Start: What Should You Do?

Outboard Motor Won't Start: What Should You Do? | Life of Sailing

Last Updated by

Elizabeth O'Malley

June 15, 2022

What might happen if your outboard engine won’t start? What you do (and don’t do) when outboards don't cooperate is key to navigating this unpleasant situation.

Despite your affinity for wind power, familiarizing yourself with the basics of why an outboard engine won’t start – whether it’s fuel issues, spark plugs, or airflow just to name a few – will make a big difference in your safe and successful outboard engine operation.

Sometimes getting from your anchored boat to shore is a matter of fun and frivolity – “Hey, why don’t we go grab a drink dockside!” or “The guidebook says that those barrier islands over there are great for finding sand dollars – how about we take the kids and go check it out!”  Other times, getting to shore is quite serious and even a matter of life or death. To ensure your outboard engine starts and keeps running take the time to learn outboard engine basics.

Trust me, as a sailing camp counselor for a decade and as a twenty-year recreational sailor on both the Atlantic and Pacific coasts, the last thing you want in either situation is to hop in your dingy and the outboard won’t start. It can range from mildly annoying to embarrassing to ridiculously frustrating to scary as hell.


Table of contents

Getting Familiar with Outboard Engine Issues

Before you find yourself in such an unpleasant situation, take some time to get really familiar with the ins and outs of outboard motors. Primarily mechanical, they are actually fairly logical pieces of equipment and if you have even a basic understanding of how they work and what to monitor and maintain, it can save your wallet, your blood pressure, and maybe even a life.

Outboard Engine Fuel Considerations

Outboard engines run on fuel. And if the fuel isn’t there (Can you say “bone dry, empty fuel tank”?) or the fuel isn’t flowing and sparking properly, then you are likely to find yourself at a standstill. So, fuel should be your first consideration relative to a healthy outboard engine.

For starters (pun intended!), fuel must be clean and new. (Yes, fuel ages as it sits because moisture is introduced to the storage container due to changing temperatures and condensation.)  Dirty old fuel often has moisture that has infiltrated it. When water is present combustion is compromised -- a spark plug can’t spark fuel that has too much water in it.

Additionally, nowadays, ethanol is found in a lot of fuel and ethanol “attracts” water molecules. Since boat fuel tanks are almost all vented, the ethanol can pull water out of the top atmosphere and right into your tank. It does not take much water at all to create problems. According to a top marine engine maker, if water-molecule concentration in a fuel tank reaches just ½ of one percent, the H20 molecules can bond to the alcohol, causing the water to sink to the low point of the fuel tank.  And guess what… at the bottom is exactly where your fuel pick-up is.

You can counteract the presence of ethanol (alcohol) in your tank by 1) using a water-separating fuel filter and 2) by adding a fuel stabilizer and conditioner in the appropriate amounts based on your tank size. This is a proactive measure to ensure your fuel is fresh and stays clean.

As a solvent (a dissolver) ethanol is also the reason that breaks down debris from containers in which it may have been stored or from tank lines through which it has been run. As you can imagine, debris anywhere in an engine is not a good thing. (Really, is there ever a time or place where debris is a good thing. I mean, it’s debris, right!?  But we digress.)  Debris will clog up various parts of an engine – and it does not take long to do that clogging – so it’s important to be aware of both the need for clean fuel and to know what clean fuel actually is.

Approach fuel the right way from the start – even before water-separating filters and fuel stabilizers and conditioners -- by actively seeking out ethanol-free fuel. You will find that some marinas do sell it and, yes, no surprise, it is a bit pricier than ethanol fuel. However, despite the cost differential for ethanol-free fuel, we suspect you will be very pleased to have spent that extra few cents per gallon if you find yourself firing up that outboard in a crisis situation.

Outboard Engine Spark Plug Considerations

Assuming you have committed to using clean, fresh fuel, another thing to consider if you want to ensure that your outboard will reliably start is whether or not the fuel is sparking – are you having a combustion failure and, if so, why?

The spark necessary to make the fuel ignite comes from a magnet-coil combination that occurs when the engine spins. Candidly, this process – much of it due to precision timing – is oretty darned complicated and often is best addressed by a good marine mechanic. But even a non-mechanic can take basic steps to ensure the spark, such a critical part of starting an engine, happens without issue.

First, it is important that the wires for the ignition – are in good shape. They should not be corroded or damaged or loose. Then, take a look at the spark plugs. Normal spark plugs are dry with a gray color. If the plug is wet, that could mean there’s water in the fuel and it may have a white residue that means that the plug is hotter than it should be. A black sooty plug means that there is too much oil in it. A visual examination of spark plugs can expose a variety of troublemakers.

Regularly check your spark plugs for damage, fouling, sooting, and corroding. Spark plugs are small and fairly inexpensive – we suggest that you keep some extra ones on hand. To clean ones that you already have installed, there are a variety of DIY hacks -- from using a blowtorch to remove carbon from the metal to soaking in carburetor cleaner online. (Our personal DIY favorite is using Coca Cola and salt!)

Something to note:  If you are not successful in starting the engine and suspect that it maybe a spark plug matter, be aware that the plug should be wet from fuel when you remove it. If the plug does not show signs of having been exposed to fuel, your problem may not be the spark plug. It is more likely a challenge with the fuel flowing (or not flowing in this instance) to the combustion chamber. (The combustion chamber is where the spark plug interacts with fuel/air to do its job and, as such, it is where the plug would become wet due to the presence of fuel).

Outboard Engine Fuel Flow

So, why wouldn’t the plug be wet from fuel? This is likely because the fuel is not flowing – from the fuel tank to the point where the plug encounters it. Check first to see if the fuel bulb gets full and hard when you pump it. If it is hard, that’s good – fuel has moved into it. To ensure that fuel is new (and not leftover fuel), you can carefully disconnect the bulb from the engine line (not the tank line) and try pumping it some more. It should pressurize – and if it doesn’t, there may be a leak which means that a new bulb is needed. While you’re in the region of the fuel bulb, you should also do a good inspection of the fuel line itself. It should not have leaks or be crimped or snarled – a kink-free fuel line is vital. (Don’t remind me about the time our grocery cooler was sitting right on top of the fuel line and it took me about 20 minutes in the pouring rain to figure that out. Sigh.)

Not only must the fuel flow through the lines, it has to be able to flow through the important fuel filter. Either look at the fuel moving from one side of the filter to the other (which is possible with translucent lines) or remove the line that exits the filter and cover the nipple up, while pumping the bulb, to see if fuel flows through the filter. If it is not flowing, you have got a blocked fuel filter that needs cleaning or replacing in order to get the ever-important fuel flow happening again.

Another area where fuel flow can be impeded is within the carburetor – and carburetor issues are typically not a project for the average Joe (or Jane). Carburetors are complex, tricky beasts but they can be tamed (sometimes) by carefully cleaning out the small fuel jets which may be blocked. Clearly, the best way to avoid a blocked carburetor problem is not getting it blocked in the first place. (Wink wink!)

Boats that sit unused for a while can experience a fouled or gummed-up carburetor. To avoid this, empty the carburetor bowl if you know you won’t be running the engine in more than 7-10 days. Simply disconnect the fuel line and run the engine until it quits, starved for fuel. For carburetors which feature a plug, you’ll just need to remove that.

If we are using fresh, clean fuel and our spark plugs seem to be in order and our fuel-flow process appears to be clear and unobstructed, then another contributing cause to an outboard not working can be a lack of air. Remember that the spark plug needs the fuel AND air to come together for that combustion to happen. An engine that is air starved is like putting a lit match under a glass. Once the air inside the glass is gone, the match can no longer burn.

Outboard Engine Air Flow

Indeed, engines need air – and so you need to check to make sure there is no air flow blockage. There are air vents in an engine’s cowl cover. (Cowl covers are important for boats for two reasons – they direct the flow of air into the engine and they keep water/moisture out of it.)  The vents are typically located on the aft side of the cowling – and are often covered with a filter or screen, sometimes they are covered with a one-direction flap.

It is vital that these airways are not obstructed. Be sure to keep them clean from any accumulation of dirt, sand, debris, adhesives, etc. (Something for you to just be aware of: most boats don’t have air filters. Generally being out on the water, there’s not a lot of dust to filter, so it’ not often there’ll be an actual air filter for a boat engine.). Boat engines need air, they just don’t necessarily need filtered air. The takeaway is that engines need air to combust so blockage of air to an engine may be a reason the outboard won’t start.

Essentially, there are four contributing factors to an outboard engine not starting:  bad fuel, bad fuel flow, bad air flow, bad sparks. By knowing the basics of what it takes for an engine to operate, realizing the importance of maintaining certain aspects of the operating system, and logically thinking through the system if and when your outboard won’t start, you’ll be a lot better prepared for this almost-certain scenario.

Hopefully, now that you’ve familiarized yourself with these four considerations, you’ll be more coolheaded, having some idea of what the problem might be rather than furious and frustrated with no idea of what’s going on.

Additional Outboard Engine Considerations

The one obvious thing that we haven’t mentioned but, of course, need to besides the quality of fuel and the flow of fuel – is the existence of fuel. We have plenty of stories (and we bet that you do as well) where, after all sorts of expletives and gnashing of teeth, an old salt pauses, scratches his head, and sheepishly checks the fuel tank.

It’s worth mentioning that a quality portable fuel tank should be CARB and EPA-compliant, be of suitable size for safe stowing and portability, feature a two-way valve for pressure release at certain PSIs, and, for those of us getting up in years, a high-contrast fuel gauge to actually be able to see and determine the fuel level. Nothing more embarrassing than reading the fuel gauge wrong and thinking you’ve got something in there only to find out that it is actually empty!

Sometimes one other (and less obvious) reason that a boat won’t start is… the kill switch is off. With the kill switch secured, the engine can run, but with the kill switch off, the circuit is broken keeping the engine from running (or, if not running, from starting in the first place). Kill switches were first included on boats in the early 1970s and have no doubt saved many many lives; they can, however, sometimes be forgotten in the emotional frustration of an outboard failing to start.  

Remember: fuel, fuel flow, air flow, spark plugs. Anything beyond those four, and you’ll likely need a professional mechanic. 

Outboard Motor Won't Start: What Should You Do?
Elizabeth O'Malley

Elizabeth O'Malley

Elizabeth has sailed Sunfish, Catalinas, Knarrs, and countless other boats. Forty years later, she finds herself back on the waters of Bogue Sound, where she lives and sails with her daughter, Morgan, and chocolate lab, Choco.

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