Features December 2006 Issue

Dinghy Engines

Few things are more frustrating than pulling fruitlessly on the start cord of stubborn outboard, or paddling your dinghy (and the $1,000 outboard strapped to its stern) back to your boat. The gradual shift away from two-stroke engines to the more durable four-stroke variety has reduced the liklihood of these moments. But the four-stroke portable engines (December 1 and March 1, 2003) we’ve tested over the last three years 4- and 8-horsepower models are big and heavy. The 8-horsepower engines, which can exceed 80 pounds, can’t even be considered truly “portable.” The 4-horsepower models (about 55 pounds) are easier on the back, but it’s still no fun to wrestle these engines on and off the transom.

From left to right, the Yamaha F2.5, the Mercury 2.5, the Tohatsu MFS 2, the Honda BF2, and the Suzuki DF2.5.

Until recently, pickin’s have been slim if you wanted a lighter, compact four-stroke: the Honda 2 and the Yamaha 2.5. But three super-small four-strokes from Suzuki, Tohatsu, and Mercury hit the market this year, giving consumers a wider range of choices.

We rounded up all of the 2- and 2.5-horsepower four-strokes available on the market: the Honda BF2, the Yamaha F2.5, the Suzuki DF2.5, the Mercury 2.5, and the Tohatsu MFS2. The Honda and the Yamaha are the most expensive, with retail prices of about $1,000. The Mercury carries the lowest MSRP ($855), followed by the Tohatsu ($927), and the Suzuki ($955). All are 15-inch shaft models.

PS used a Walker Bay RID 275R to test the five engines. A review of this 9-foot, hard-plastic dinghy appears in the November 2003 issue. The Walker Bay uses an inflatable tube around its exterior for stability when the boat is fully loaded. It weighs 89 pounds, has a beam of 5 feet, 8 inches, and is rated for up to a 4-horsepower outboard. The boat can be fitted with either a PVC or Hypalon tube. (Cost: $860 with the PVC tube; $1,200 with the Hypalon tube.)

The test site was a saltwater basin just south of Tampa Bay, Fla. We used a friend’s waterfront dock as a staging ground for the test. Testers fixed a 2-inch by 8-inch board be-tween two of the dock’s pilings, so all five engines could be mounted side by side. We examined all components and critical access areas, including oil fill and oil dip stick, carrying handles, tillers, throttles, forward/reverse shifts, cowlings and their clips and fasteners, and ease of tilting, etc. Testers then moved the engines to a second 2 x 8 mounted just a few feet above the water (pictured above). There, the engines were started and run through part of their break-in periods. Testers also evaluated ease of starting at this point.

Once the engines were broken in, they were mounted one at a time on the Walker Bay for speed and noise testing, which took place with two people on board. Speed and noise data were recorded at idle, half-throttle, and full-throttle settings. Interestingly, there was no difference with any of the engines in thrust or speed, at half throttle and full throttle. Therefore, only idle and full-throttle numbers appear in the chart on page 26. Speed and noise levels were taken in two directions and averaged to account for wind and current.

We had three testers (two men and one woman) start each engine to assess smoothness and ease of starting. They mounted, lowered, and tilted the engines, then operated them on the boat, and finally removed them from the boat. This gave testers a start-to-finish experience with each motor. At the rate these small units burn fuel, any gas economy advantage would be negligible, so we did not test fuel consumption.

When we weighed each engine, all but the Mercury  (4 pounds over its listed weight) and Tohatsu (2.5 pounds over its listed weight) were within a pound of their published weight.

The weights of these mini motors ranged from 29 to 42 pounds. These are all one-cylinder engines with pull starts and integral fuel tanks that hold about a quart of gas. The engines require only about 10 ounces of oil, and the gear cases even less than that. Four of the five engines carry the three-star exhaust emissions rating (the best you can get). The Yamaha has a lower, two-star rating, which is defined as very low emissions.

All are water-cooled engines except for the Honda, which is air-cooled, meaning it runs louder than water-cooled engines but doesn’t need to be flushed with freshwater. The others have water pumps that must be replaced, typically at 100 hours.

As is the case with all portable four-strokes, these engines must be stored in a particular position to prevent engine damage resulting from oil draining out of the crankcase. All can be stored in the upright position or on one specific side. The Yamaha can also be stored resting on its face with the prop up. It has built-in resting pads on the front of the engine specifically for this purpose.

The Honda was the only engine with a centrifugal clutch rather than a separate shift lever. Simply turning the throttle executes the transition from neutral to forward. The other four engines have starboardside gear levers with neutral and forward positions.

Another commonality: All five have oil-check win-dows. All except the Yamaha’s are viewable without removing the cowling.

All of these engines have tilt support pins that are used to you guessed it support the engine when it’s in the tilted position. The Mercury and Tohatsu pins are easiest to operate you simply pull them out, tilt up the engine, and push it in.

Testers found minimal variations among the engines in speed. The extra 0.5 horsepower of the Mercury, Suzuki, and Yamaha had little to no effect on speed. We didn’t measure thrust, but testers reported that no engine had more “umph” than another. There were some differences in noise levels, which we will address in each product review.

Testers noted significant distinctions while carrying, mounting, and starting the engines. (All have chokes, stop buttons and kill switches with lanyards.) Differences in throttle operation and ease of tilting are also noted below.

The Suzuki, which was introduced earlier this year, and the Honda are the lightest and most compact engines tested.

Testers were disappointed with the Suzuki’s thin handles for its clamp screws. They’re nothing more than 2-inch-long metal pins. The DF2.5 has a nice grab handle in the front, but the back of the engine has no handles, so carrying the engine in an upright position is awkward, in our opinion. There’s no recessed handhold area in the top of the cowling’s backside for tilting and lowering the engine once it is mounted on the boat.

Two rubber straps are used to secure the cowling. They can become slippery and difficult to hook and unhook if your hands are wet or greasy.

The starboard gear shift is smaller than we prefer, and testers said it was harder to reach than the other three models with shifts.

The Suzuki must be stowed on its port side, so it lies on the elbow of the tiller and a “case protector” (a bump in the cowling).

The Suzuki was the second-loudest engine in the group. We recorded 97 decibels at wide-open throttle (WOT), which is only two decibels short of the air-cooled Honda. Noise levels at idle 77 decibels were also higher than the other water-cooled models.

Testers gave the Suzuki a Fair for ease of starting because the engine had a strong recoil effect. Each owner’s manual directs users to pull the cord slowly until resistance is felt, then pull the cord briskly to start. If this first step is not taken and the cord is pulled vigorously from its original position, it can recoil or snap back and pull your hand back toward the engine. This recoil effect was most prominent with the Suzuki, it happened a couple of times to our testers while starting it. It is absolutely necessary to follow the starting instructions.

The owner’s manual calls for engine and gear case oil changes at 100 hours, and spark plug and water pump replacement at 200 hours.

Bottom Line: The attractively priced Suzuki is light, but it’s loud and needs beefier mounting clamps and a backside carrying handle. Starting the engine can be tricky.

The Yamaha is eight pounds heavier than both the Suzuki and the Honda, but five pounds lighter than the Mercury and Tohatsu.

Testers didn’t mind the Yamaha’s traditional, floppy-ear-clamp style mounting screws. They also thought this engine had the best means of securing its cowling: two large clips, one on the back and one on the front. There’s no recessed handhold area on the cowling top to make it easier to pull the engine out of the water, however. For carrying the engine in a vertical position, there is a handle on the back and a recessed area below the front cowling clip. The Yamaha must be stored on the tiller side or face-down with the prop facing up (as noted earlier). It has no cover protector, and the manual suggests placing a towel under the engine to prevent scratches.

Testers liked the large gear shift, and reported that it moved smoothly in and out of forward. It’s also a few inches farther forward than the Suzuki’s, making it easier to reach. The Yamaha, Tohatsu, and Mercury have longer tillers and larger  throttle grips than the Honda and Suzuki.

The Yamaha was a smooth starter, and it was among the quieter engines in the group. In fact, it had the best score at WOT: 91 decibels.

The manual calls for engine and gear case oil changes at 100 hours, and spark plug and water pump replacement at 200 hours. The manual needs a better illus-tration to identify the oil plug drain, in our opinion.

Bottom Line: The Yamaha is easy to start and shift, and we like the longer tiller. It’s also relatively quiet. On the downside, it’s the second most expensive motor, requires tiller-side horizon-tal storage, the cowling must be removed to see the oil inspection port, and it has a lower emissions rating.


None of the engines has a reverse gear, and there’s really no need for it. When you want to back down, just spin the engine around.

The Honda is the most expensive engine tested. It and the Suzuki are the same weight, and roughly the same size, but the Honda is equipped with better carrying handles, in our opinion. It has a handle on the front and a recessed area below the backside of the cowling. It was by far the easiest engine to transport from dock to boat and back.

On the other hand, the Honda’s cowling was the toughest to reinstall. The cowling is too flexible, and positioning its two metal tabs into slots on the engine’s front is tricky (the back is secured with a rubber strap similar to the type on the Suzuki). If the tabs aren’t in correctly, the backside of the cowling won’t fit properly. When we returned the engine to the Honda dealer, he set us straight, showing us how to make it work.

Handles for the mounting screws are double-ended eyebolts. These  are easy to padlock and will likely last longer than the floppy ear types.

The engine can be stored on two hard-plastic case protectors on the starboard side. The protectors are larger than on the other motors so the engine is more stable, and they are ribbed for better traction.

The Honda was easy to start. At first, testers found the centrifugal clutch awkward, but quickly grew to like it, and ended up preferring it over the engines with a separate gear shift. The clutch allows the driver to hop back and fourth from forward to neutral. This is very useful while pulling the dinghy up to a dock or its mother ship.

The manual states that some of the clutch components should be replaced after 150 hours. The technical staff at Defender Industries in Waterford, Conn., a large seller of small engines and boats, tell us that this practice is rarely done. Mechanics there have never had to replace a clutch.

Downsides: The Honda has the shortest tiller and it was the loudest engine. In addition, the BF2 is the most expensive. The manual calls for more frequent oil changes every 50 hours than the others.

Bottom Line: It is loud and it’s the most expensive engine tested. But the Honda is still our top pick because it excels in the areas we think are most important weight, portability, storage, and starting. Plus, you don’t have to flush it.

The Mercury 2.5 and Tohatsu MFS2 are identical in size and shape, but Mercury points out that its engine is not just a rebranded product. “The 2.5 is a joint development effort between Mercury and Tohatsu, with Mercury engineers as fully involved in the design as Tohatsu’s,” said Mercury spokesman Erik Pope. “The product is then manufactured by TMC, the joint venture company that manufactures the product for both companies. Differentiation in horsepower is obtained through different carburetor geometry.”

The two engines are noticeably larger and heavier than the three others, and therefore they were harder to carry and mount on the dinghy. The Mercury is the least expensive engine, and the Tohatsu is only about $50 more than the Mercury.

The Tohatsu and Mercury have identical systems of securing the cowlings: Both have a single clip on the back and the front is held in place with a single tab that slides into a recessed area on the lower cover. They lack a recessed area or handle on the back, which makes carrying these engines in a vertical position difficult. The Mercury and Tohatsu have the same floppy-ear style handles on their mounting screws as the Yamaha.

Like the Honda, the Mercury and Tohatsu can be stored horizontally on their starboard sides, resting on two cover protectors for stable stowage.

The Mercury was very easy to start. One tester did not have the strength to start the Tohatsu, however. We like the long tillers and large, grippy throttles on these engines. The large shift levers that are close to the front of the engine are easy to reach.

The Mercury is rated at 2.5 horsepower compared to the Tohatsu’s 2 horsepower, but the Mercury pushed the dinghy only one-10th of a knot faster that the Tohatsu at WOT. Noise levels were nearly identical as well. Both engines, along with the Yamaha, were much quieter than the Suzuki and Honda. Overall, they ran slightly smoother than the other engines, but both the Mercury and Tohatsu made a slight rattling sound at idle. Mercury said the engine we tested is a prototype and that the rattling issue has been corrected.

The Mercury manual instructs the user to replace the engine and gear case oil and spark plug at 100 hours. At the same time, a dealer should replace the water pump and lube the splines on the driveshaft. The Tohatsu manual calls for the same maintenance but says nothing about lubing the driveshaft.

Bottom Line: They’re larger and heavier than the others, but we like their long tillers, large shift levers, and simple tilt support pins. The Mercury, which has the lowest price and was easier to start than the To-hatsu, earns Budget Buy honors.

If light weight is a priority, then the larger, heavier models from Mercury and Tohatsu are not for you. However, if the engine will spend long periods of time on the dinghy, the low-priced Mercury is an attractive option, in our view. It’s a smooth-starting, relatively quiet engine with a long tiller and comfortable throttle. Our test engine rattled a bit at idle that’s the only performance drawback. The Tohatsu was harder to start, and it has a higher retail price, so we’d go with the Mercury.

Among the smaller engines, the Honda is our top choice. Considering all of its positives (lightweight, compact, easy to stow, easy to start, and centrifugal clutch), we can deal with its noisier operation, short tiller, and fussy cowling. The Suzuki and the Yamaha have some significant pluses, but they come up short in too many areas that are important to us.


yamaha-motor.comHONdA, 770/497-6400 




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