Four-Horse Four-Stroke Run-Off
Suzuki edges Yamaha and Mercury with a little more kick, a long and easy-to-operate tiller, and one-pull starting.
In March of this year, Practical Sailor covered small four-stroke engines in a market scan of the 4- to 9.9-horsepower range. This roundup featured 30 different engines and was loaded with data and specifications obtained from dealers and manufacturers. Many of the engines were inspected in dealer showrooms, but we did no field testing.
Since then, we've had a chance to hit the water with some of these engines. Two of our editors spent a full day with the three 4-hp four-strokes shown at right. They were lifted, mounted and removed, carried, started, run, checked for features, and examined under the hoods. Basically, we got to know them well.
The idea (not to say full-blown plan) is to test all of the engines listed in that March market scan—one group at a time, though. This will allow close examination of each. It also avoids the logistical nightmare of trying to break in and test 30 engines at once. Actually, we won't have to operate 30 different engines, because many small engines are identical even though they carry different brand names.
What We Tested
We've actually covered six 4-hp engines by testing only three models: the Suzuki, the Yamaha and the Mercury. They're all single-cylinder engines with 15" shafts. Honda does not make a 4-hp model.
Suzuki loaned us a DF 4, which is the same motor as the Johnson 4. (The Johnson 9.9 is also a re-branded Suzuki. Bombardier does make its own 6- and 8-hp engines.) West Marine in Sarasota, FL, was kind enough to supply a new Mercury 4. This engine is built by Tohatsu, which also markets it as a Nissan. Finally, we purchased a new Yamaha 4 from The Boat Center in Miami, FL.
Since some of the manufacturers use the same powerhead for their 5- and 6-hp versions, most of the comments concerning the 4-hp models would apply to their higher horsepower brethren—not performance, of course, but certainly ease of carrying, storage, and access to maintenance components like oil fill and spark plugs.
How We Tested
We put each engine on a 10-foot Apex inflatable and ran it at various throttle settings with one or two people aboard. Various ratings were given based on the tests.
The first in the accompanying chart is a portability rating: How easy was it to carry? Next, installation ratings were assigned. We tied off the Apex next to a 25' Contender powerboat, and with one person on the Contender and one in the dinghy, we handed the engine over and installed or removed it as needed.
After tightening each engine to the transom, connecting an external fuel tank, and adding or checking crankcase oil as needed, we started each engine. The ease-of-starting rating was based on numerous attempts—cold and warm—throughout the day.
Next, if an engine needed to be broken in, it was. The son and godson of one of our testers helped out here, saving us a lot of time puttering around under the hot Florida sun. Two hours was the minimum break-in time required by both Mercury and Yamaha. After that, the break-in period allowed for short bursts at wide open throttle. The Suzuki was already broken in.
Testing and rating engine operation and noise (at idle and mid-throttle) were done in a calm-water channel in Key Largo. Once in the ocean, we evaluated each for performance and noise at wide open throttle. Upon return to the docked Contender, we tilted and lowered the engines, examined their hood latches, looked at spark plug access, and then removed the engine.
Their storage positions were checked for stability and oil and fuel leakage. We did not conduct speed testing with any of the engines, figuring that if you're buying a 4-hp for a dinghy, or as transom power on a small sailboat, minor differences in speed are not critical.
Similarly, these engines consume so little gasoline that measuring and comparing fuel flow rates seemed a bit pointless. The differences might amount to a couple of dollars a year, assuming a lot of run time.
Testers used a bathroom scale to verify the weights of each engine. Powerboat Reports editor Chris Landry weighed himself, and then weighed himself again while holding each engine. Certainly this is not the most scientific test, but good enough to determine if any of the manufacturers' stated weights were grossly inaccurate. None was.
All were tested with standard manufacturer propellers for dinghy use.
What We Found
Some commonalities: All vibrated noticeably at mid-throttle settings, a result of their single cylinders; all had throttle friction lock and steering friction lock; and all lock in the down position when shifted into reverse. We made sure of this by slamming each engine into reverse and cranking the throttle. None of them kicked up.
The bathroom scale said the Mercury weighed 57 pounds, two more than the stated weight. The engine did have a full crankcase of oil and some fuel, which probably accounted for the difference.
A single handle is located at the front of the engine, and there's an indentation at the rear of the case to assist lifting and carrying. The front handle offers no hand protection and digs into your skin. This makes carrying and maneuvering a bit difficult. It would be better if a handle replaced that backside indentation.In the storage position the Merc is stable; it rests on a single pad (just below the cowling), its throttle, and its prop.
The hood easily comes off with a single latch located at the rear of the engine. The oil fill and dipstick, combined on a single screw-on yellow cap, is located on the starboard side toward the front of the block, and is fairly easy to access.
Since this engine was new, we had to use the fill and add the crankcase oil. Because the fill location is behind a few wires, you'll need a funnel with a long neck or hose attached. We had a shorter one and spilled some oil. The single spark plug is on the back of the engine, and is easily reached.
The Merc started on the first pull and continued to be easy to start throughout testing. While running during the minimum two-hour break-in period, it stalled a few times at idle. The idle setting from the factory was too low and needed some adjustment. We used a screwdriver to increase the idle and it didn't stall again. The manual does not have any information on adjusting the idle, so those less technically capable owners might end up bringing their motor back to the dealer. Something this simple should be in the operating manual—it's in both the Suzuki and Yamaha manuals.
The tiller is a short one (12 inches off the transom of the inflatable), compared to the other two, and it's not angled toward the driver.
Performance was strong; planing speed was attained with one person aboard and the boat almost planed with a pair of 200-pounders. The side-mounted shifter was clunky to operate—not as smooth as the Yamaha or Suzuki.
Noise levels were comparable on all three engines, with the Merc registering 67 decibels at idle, 81 at mid-throttle and 89 at full throttle. The Mercury has an internal tank and a fitting for an external tank.
Bottom Line: We really like the strong performance and easy starting of the Mercury, but not the clunky shifting and short tiller. The low idle was easily adjusted, but should have been explained in the manual.
Like the Mercury, the Suzuki 4 is a single-cylinder 4-stroke with a stated dry weight of 55 pounds. It weighed 58 pounds on the bathroom scale with full oil and with the internal fuel tank about half full.
The single carry handle on the Suzuki 4 is located at the rear of the engine. When carrying it vertically or putting it on and off the transom, we used the base of the throttle handle as a secondary gripping point. This is uncomfortable. It's the reason for the Suzuki's low portability rating.
The Suzuki rests nicely on two side-mounted storage pads and its propeller. The hood fits snugly on this engine and is held in place by two latches, one in front and one at the rear. The oil fill/dipstick is easy to access. There are even instructions printed nearby on how to read the dipstick. As with the Merc, a funnel with a long neck or hose attached makes spillage less likely. The single spark plug is on the back of the engine and easily accessible.
One-pull starting was the norm once the Suzuki warmed up. The tiller arm is the best of the group—it's angled outboard and extends 17 inches from the transom.
Full-throttle performance was on a par with the Mercury. The Suzuki planed the dink easily with the heaviest tester alone and nearly so with both testers aboard. Shifting is clean and crisp. Tilting the engine up and down is easy. We noted no sticking or jamming. Noise levels on the Suzuki were 70 decibels at idle, 79 at mid-throttle, and 88 at wide open throttle.
The Suzuki has the largest internal fuel tank (nearly half a gallon) but has no external tank connection.
Bottom Line: The Suzuki is our top pick because of its performance, tiller handle, and easy starting. It's not perfect though. It needs a second handle at the front to make lifting and carrying easier. Plus, the plastic steering friction lock was difficult to turn and adjust.
The Yamaha is the lightest engine in our test group. The manufacturer claims a dry weight of 49 pounds. The bathroom scale read 50 pounds with oil and fuel.
With rubber-coated carry handles, one located forward and the other aft, and a lighter weight, the Yamaha was by far the easiest engine to lift, carry, install, and remove.
The Yamaha's storage, starting, and performance were not on par with the other engines, however. With the Yamaha in its storage position, it lies awkwardly on its handle and tips to one side or the other. Some type of additional material—a chunk of Styrofoam, a towel or two—would be needed to stabilize it.
Unsnapping two latches, one forward and one aft, allows you to remove the engine hood. Access to the oil fill and dipstick is good—it's a screw-in unit similar to the other engines. Spark plug accessibility is only fair on the Yamaha. The plug is at the bottom of the engine on the starboard side and is hard to reach.The Boat Center in Miami loaded the engine with oil and gas, then test ran it for us—it took the mechanic 13 pulls to get the engine started. Even after the minimum break-in period, we found the Yamaha more difficult to start than the other two engines.
The tiller arm on the Yamaha is similar to the Mercury's, but an inch longer off the transom. The performance was not as strong as the other two engines, with planing only possible with our lightest tester aboard. The small shifter sits in a recessed channel on the starboard side. Shifting was smooth and crisp.
Tilting the engine up was easy, but we did have some difficulty lowering it—the latch seemed to stick and not release cleanly every time. Noise levels were on par with the others: 69, 79, and 90 decibels at idle, mid-throttle, and wide open, respectively. The Yamaha does not come with an external tank but has a fuel fitting for one.
Bottom Line: If portability is your primary concern, this is the engine for you. Drawbacks on the engine tested included harder starting, less power than the others, and a finicky tilt lever.
Some debate ensued before the final vote was in. All of the engines have their drawbacks and strengths, so it was necessary to prioritize the pluses and minuses before making conclusions.
In the end, we rated the operational aspects slightly ahead of portability. The fact is, none of the engines is fun to carry around or put on the transom of a boat, though the Yamaha is easiest.
The Suzuki, with its easy starting, solid performance, smooth shifting and long tiller, is the top pick. Its drawback—no front carrying handle—can be dealt with. Just keep a glove around to protect the hand that endures the tiller elbow.
The Mercury comes in a close second, held back by its somewhat rough shifter and no backside-carrying handle.
The Yamaha finishes third. It may be easy to carry, but it doesn't stow in a stable position, was harder to start than the others, and exhibited less kick than the Mercury and Suzuki during our day of testing.
The other thing going against the Yamaha is price. We were able to find both a Suzuki 4 and a Tohatsu 4, identical to the Mercury, for around $900 on the Internet (see the chart).
The cheapest Yamaha we found was $999.
But again, if portability is your main concern, the extra money might may well be worth it.