The Care and Feeding of Your Dinghy Outboard

By using clean fuel and performing regular maintenance, your outboard motor should give you years of trouble-free service.
By using clean fuel and performing regular maintenance, your outboard motor should give you years of trouble-free service.
By using clean fuel and performing regular maintenance, your outboard motor should give you years of trouble-free service.

There is nothing quite so discouraging as finding your outboard motor won’t start after a period of non-usage, or even worse, after arriving in a new port with our anticipation of dinghying ashore to do some exploring. We have all been there, cursing at our non-functioning motors as we slowly row off while our crew pretends they aren’t noticing. 

Don’t be Fuelish
However, there are a few simple things you can do to avoid outboard despair. The basic requirements of any gasoline-powered internal combustion engine are clean fuel, clean air and a good spark at the right interval. Of course, there are more nuances for each requirement, but begin with the basics.

A cardinal rule of purchasing gasoline is to do so at places that pump a lot of fuel. Obviously, for many cruisers, that will be a marine fuel dock, but be wary! Smaller, sleepier marinas may not turn over their fuel supplies rapidly. As a general rule of thumb, gasoline with ethanol can be stored safely for up to three months without significant deterioration, and non-ethanol gasoline up to six months. I was a member of a small yacht club once that received only one or two loads of fuel for each six-month season (in the Northeast), and they sold only ethanol gas. Needless to say, I didn’t purchase gasoline from the club after a long winter of sitting in the ground.

Top Tier keeps outboard carburetor jets clean.
Top Tier keeps outboard carburetor jets clean.

For outboard gas, often the best and cheapest way to purchase it is at a regular gas station ashore where you can easily observe the rapid turnover assuring fresh fuel. In addition, the major oil company brands have strict storage guidelines for fuel that might not be as carefully followed at smaller mom-and-pop marinas. I purchase only TopTier automotive gasoline brands whenever possible. These are companies that guarantee a higher level of additives that promote cleaner burning. Go to to learn more. In New England, where my boat is currently based, numerous gas stations feature TopTier brands, including Sunoco, Mobil, Shell and others.

In addition, you will see some marinas advertise specific additives at the pump, like ValvTect, for example. If the marina is busy, pumps lots of fuel and is also ValvTect branded, it will be superior to what you’ll get at a sleepy fuel dock with no branding. Marinas have to maintain certain standards to be able to display the branding and the additives are probably helpful.

You may have heard many people say all gasoline comes from the same terminals, so there is no difference between the cheap off-brands and the name brands. Unfortunately, this is not the whole story. Yes, a tanker truck may fill up with gasoline that is then delivered to several different stations, including your marina, but name brands all have their own blends of additives that can make a difference in performance. It is my understanding that if you see a name brand on the sign, the gas in the ground will have its additive package.

When long-distance cruising, you may be limited in your choice of where gasoline can be purchased, but there will almost always be local fishermen about. Observe or ask where they get their gas. Their livelihoods (and their lives!) depend on the proper functioning of their motors, and you can be sure they know where the gas is good. I have even purchased gasoline and diesel directly from fishing boats when there were no other alternatives. Good old U.S. dollars tend to be welcomed anywhere.

Cruisers who spend some time in the area are also great sources of information. Sometimes there just isn’t a good place to get gasoline, so carry plenty of spare fuel in proper storage containers. If forced to purchase gasoline of suspect origins, I like to pump a bit into a glass jar first. I let it settle for a few minutes to see if there is observable crud or water in the gas. There are funnels with filters in them, but I have found the fuel flow is too slow to be practical. When in doubt, don’t use the gasoline. I would rather row ashore than risk damaging my engine.

I personally prefer to use proper plastic fuel jugs using the universal color scheme of red for gasoline, yellow for diesel, and blue for water. Even if you don’t make mistakes, someone else handling your cans might! Write your name or your boat name on the jugs. If a jug is for a 2-stroke, I label it so I don’t mix it up with straight gasoline. In addition, I always go through a rather formal ritual when at a fuel dock to make sure I am getting the fuel I want. Hoses can get crossed easily, nozzles can look alike and attendants can make mistakes. If I am handed a fuel nozzle, I always ask, “This is gasoline, correct?” I also try to track the hose back to the pump just to make sure, and I pump my own gas whenever possible.

Tip over the nozzle and let whatever is in there drip out before inserting it into your gas can or tank fill opening. There should be only a tiny amount of gas in the nozzle, usually a few drops or less, but I have had the unpleasant surprise of a gush of water mixed with fuel pour out from a nozzle left in the rain unprotected. Water in your gasoline is the major problem leading to a non-starting situation. I’ll write more about that later.

Some time ago, environmental regulations mandated non-venting fuel jugs, which required special spigots with valves that were often hard to use and resulted in lots of fuel spillage in use. However, I have found the current generation of non-venting jugs is far superior to the early ones that generated a lot of bad stories. Do yourself a favor: if you haven’t purchased jugs in a few years, get some new ones. They are far superior to the ones available just five years ago. 

Plastic fuel jugs have limited lifespans, especially on boats in the tropics where the sun will speed up deterioration. Unfortunately, on most boats there is no safe place to store gasoline other than on deck in jugs, often lashed to the lifelines. On our 38-foot boat traveling to the southwest Caribbean, we found that two five-gallon jugs plus the three-gallon outboard fuel tank were sufficient for our needs with an eight-horsepower, two-stroke outboard pushing a 10-foot inflatable. Many people today are using four-stroke outboards, which in my experience burn half as much as older two-strokes.

It is not uncommon to see experienced cruisers utilize dedicated fuel jugs and tank covers made of sun-resistant cloth. Personally, I have never done so, and I find that plastic jugs are good for at least four or five years, even in the tropics. Often by that time, one or more of the spigots are in need of replacement anyway, and I find replacing a couple of jugs not a major expense. However, covering the tank that lives in your dinghy might be worthwhile since its failure in some out-of-the-way place could be very unpleasant. One backup that must be carried is a complete fuel hose with bulb, as those do regularly rot out in the sun and again could mean a total no-go situation if not working.

Sta-Bil adds life to your outboard motor gasoline.
Sta-Bil adds life to your outboard motor gasoline.

Maintain Stability
With either two- or four-stroke motors, the first thing that goes into any empty gas jug is the appropriate amount of Sta-Bil 360 Marine (the blue stuff) fuel stabilizer. I never run untreated gasoline, and I have been using this company’s products for decades in my outboards, my motorcycle and my snowblower. Sta-Bil allows you to store fuel for up to a claimed 12 months, and I have even used two-year-old gasoline in my outboard with no ill effects. Living in the Northeast, I bring my outboard gas home in the winter for use in my snowblower. If any is left in the spring, I put it in my car. Do not do this if your outboard fuel has two-stroke oil in it! Excess oil can damage your catalytic converter, but stabilizer in the fuel is fine. Obviously, there are other products on the market, but I have had great results using Sta-Bil.

Sta-Bil also claims the product reduces problems with ethanol gasoline, but your biggest worry there is keeping water out of the gasoline in the first place. Many people complain about problems with ethanol gas because ethanol bonds with the water, causing something called “phase separation.” Essentially, you end up with gunk on the bottom of your tank made up of ethanol and water with gasoline on top. The motor sucks up the gunk and you have a dead motor, and if you leave it in your carburetor, it causes corrosion that can plug everything up. If you open up your carburetor and it is full of green gunk, it is probably due to water in the gas combining with the ethanol. The green color is due to corrosion of the carb. Sta-Bil helps prevent corrosion, too.

Needless to say, this situation must be taken care of. You’ll have to clean or replace any fuel filters. Soaking your carburetor parts in gasoline can do the trick, and I find blasting some WD-40 through the tiny jets can be the easy way to clear them. Four-stroke motors burn very little gas, especially at idle, so the low-speed carburetor jet has a really, really tiny hole to let through small amounts of fuel. The teensiest piece of crud can plug that jet, making the engine hard or impossible to start. On a couple of motors, I figured out how to bypass the stop that prevented starting the engine at high throttle settings, meaning the high-speed jet was in use, and I could start the engine with a tremendous roar. That’s a temporary measure, so learn how to remove your carb and clean it! 

The carb is the part on your motor that stops you from going and is the likely culprit for poor running once started. Most modern outboards have very reliable, sealed electronic ignition components, and they either work or need to be replaced. Look to the fuel system first if your motor isn’t working right. It is even desirable to carry a complete replacement carb onboard, since you will have to service the present unit at some point. It is easier to swap in the spare and then clean the other unit at your leisure.

Adding an inline fuel filter can make a big difference in preventing crud reaching the engine in the first place, and even better is mounting a fuel/water separator spin-on filter on the inside of the transom. Luckily, carburetors are gradually disappearing, and there are many larger engines with Electronic Fuel Injection (EFI). We’re gradually seeing EFI migrate down to dinghy-sized motors, too, and by all accounts these engines suffer from fewer fueling problems. However, the beauty of an old-school carb is that it is a purely mechanical device that can be serviced and replaced almost anywhere in the world. EFI systems are computer controlled with all the advantages and disadvantages of modern digital systems. The main disadvantage is that troubleshooting and repair (often just replacement) is limited to dealerships with the right equipment.

The most important thing for your fuel system is to keep water and crud out in the first place! Assuming you’ve purchased clean gas, make sure to store it only in dedicated fuel jugs that seal perfectly—no loose lids or exposed openings! To keep the water out, I’ve found the new, non-venting jugs are far superior to older jugs with air vents that always broke or popped open.

Be sure to close any air vent on your outboard tank left in the dinghy, and also the air vent on motors with internal tanks. I close these vents immediately after I shut down the motor for even the shortest run. Also, never leave the tank in a dinghy that might be unattended for a long period. After periods of heavy rain, I always see gas tanks floating around in dinghies, sometimes upside down or even held under water by something. A friend used to leave his tank in his dink, no matter what. One day I saw him on the dock wondering why his motor wouldn’t start. After much futzing with the motor, I drained his carb and observed mostly water emerging. I took a look at his gas tank, which had probably a quart of water in the bottom!

Obviously, two-stroke motors will need the proper amount of the proper two-stroke oil added, and I put it into the jug along with the Sta-Bil when empty. In other words, no jug goes to the fuel dock without two-stroke oil and Sta-Bil. Two-stroke oil also acts as a stabilizer, but I have always used both products together with perfect results after storing fuel for long periods. Since you will be dead in the water without two-stroke oil, be sure to carry plenty. You can’t always count on it being available, but there will usually be another boater around who can lend you some in a pinch. Again, ask a local fisherman if you need to find some.

Flushing your outboard with freshwater reduces corrosion.
Flushing your outboard with freshwater reduces corrosion.

Fuel integrity will prevent a lot of outboard problems, but not all. Every cruiser needs to bring along certain essential spare parts in addition to the already mentioned fuel hose with fittings. Number one would be multiples of the correct spark plugs for your motor. Two-stroke motors go through plugs faster, and in the past I used to carry at least a couple of spares right in the dinghy along with maybe six or eight changes onboard the mothership. Four-strokes do not burn oil if they are working properly, and that avoids a lot of plug fouling. However, you should always carry at least a couple of spark plug changes’ worth of spares. I change them at least once a year. 

It is worthwhile to pull off the spark plug wires on a new-to-you motor and to apply a touch of dielectric grease to the inside of the rubber boot where it will contact the plug. This helps prevent the rubber boot from sticking to the spark plug. Dielectric grease is not conductive, so keep it away from the metal tip of the plug and the metal socket within the rubber boot to avoid adding electrical resistance. 

It is a good idea to back out your spark plugs at least once a year or so and take a look at them, even if you don’t replace them. This also guarantees the plugs don’t get frozen into the head. After I torque the plugs back in, I spray some lubricant in and around the base of the plug to help prevent corrosion. It is advisable to back out and lubricate lots of exterior bolts and screws on the motor. For example, the lower-unit drain bolts should be backed out and lubricated with a waterproof grease at least once a year, or when the lower-unit oil is changed. Also, that particular oil is another spare to carry. I also put waterproof grease on the transom bracket bolts and adjustments. Green Grease works well, but waterproof wheel bearing grease is also good.

Four-stroke motors will require periodic changing of the crankcase oil, so again carry spares for at least two changes. Though not what your factory outboard handbook recommends, I have found that ordinary automotive synthetic motor oil performs the best over the long term, and you do not have to pay a premium for the outboard name brand. The main criterion to match is the required motor oil weight, such as 10W-30 or 10W-40. Yes, there are marine-specific brands that cost a lot at a marine store, but I am not convinced an oil that is approved for your $50,000 car (of the proper weight) would not be just as good, and it will be a fraction of the price at an auto parts store. There is nothing going on inside a 4-stroke outboard motor that makes the engine innards any different than the workings of a motorcycle, car or snowblower.

It’s not everyone’s favorite product, but I find a general spray down with WD-40 all over the engine under the outboard cover does help prevent corrosion. There are other marine-specific general spray lubricants that may or may not be better, but I like the fact WD-40 does not leave a lot of residue behind. I have done this for decades, and it helped keep a 9.9 horsepower Yamaha going for 12 years pushing around a 32-foot catamaran, and I recently retired a 15-year-old Johnson 8 horsepower two-stroke that was used heavily. Both motors were running perfectly when either sold or given away. I find that WD-40 does not harm the wires or electrical components. While inside the engine cover, pay particular attention to any moving cables, rods, levers and gears that control things like the throttle or gear position. Contact points may require a little grease. I find lower-unit grease in the tube is perfect for this. For the transom bracket bolts, use Green Grease.

By observing fuel integrity, corrosion prevention and basic maintenance, you should get many years, even decades, of reliable use from your dinghy outboard. ν

Contributing editor John Kettlewell has cruised the waters between Labrador and South America for over 45 years.