Suzuki DF140 Outboard

Suzuki Marine introduced a new DF140B in 2022, not long after the DF150A/DF175A outboards hit the water. This latest 140-hp incarnation has deep roots, going back over 20 years.

Suzuki Marine introduced the DF140, their first 140 hp four-stroke and the first four-stroke outboard in this horsepower category, all the way back in 2002. When Suzuki enters a market segment, it has a penchant for doing so with a technically impressive product. While there was no other brand competing in this bracket at the time, the new 140 continued Suzuki's tradition of technical superiority.

The initial 140 — designated DF140 by Suzuki — was essentially a pumped up version of the 90/115 four-stroke in-line-4 that was introduced in 2001. This begs the question: How did Suzuki pull another 25 horsepower from the same block? In principle, to increase horsepower, it is necessary to get more fuel and air through an engine. There are several ways to do this, and Suzuki employed most of them. The easiest way to increase horsepower is to add displacement, and the major difference between the 115 and the 140 is a bore that grew from 3.3 inches to 3.4 inches. This boosted displacement from 119 to 125 cubic inches. The stroke remained the same in both engines, eliminating the need to retool the crankshaft. Another way to get more fuel and air into an engine is to turn it faster. Accordingly, the wide-open-throttle (WOT) operating range increased from 5000 to 6000 rpm for the 115, to 5600 to 6200 rpm for the 140. You may notice that the rpm band was narrower for the 140 (600 rpm) than it was for the 115 (1000 rpm). This is due to an aggressive cam profile on the 140 that provided more valve lift and longer duration.

Finally, horsepower can be increased if the intake air can be kept cool and thus denser. This is not always easy, since intake air often passes over a hot engine block en route to the combustion chamber. To help keep the engine block temperature as low as possible, Suzuki added a water-cooled oil reservoir. Company engineers also designed the cowl to route cool, outside air from the rear of the cowl directly to the intake manifold and expel hot air from the block through vents in the side of the cowl. Besides adding horsepower, Suzuki also reduced the weight of the 140. A redesigned clamp bracket and trim system shaved off a few pounds, helping the 410-pound DF140 long-shaft (20-inch-shaft) weigh in at 6 pounds less than the 90/115.

One of the most unique features of the engine, also shared with the 90/115 hp model, was the offset driveshaft. The crankshaft centerline sits forward of the driveshaft, which is driven through a set of gears. This moves the engine's center of gravity forward for better balance. The gear reduction at the junction of the block and tower housing is 1.24:1.

The cam chain is driven from the driveshaft sprocket. The cams must turn at half the speed of the driveshaft, and with initial gear reduction between the crankshaft and the driveshaft, the sprockets that drive the cam can be smaller. This results in a more compact package to fit outboard splashwells designed for any two-stroke in this horsepower range. Additional gear reduction in the lower unit provides a 2.38:1 overall ratio at the propeller. Also borrowed from the 90/115 were a water-cooled, long-track intake manifold; cooling fins in the flywheel for the alternator and magneto; 40 amp alternator; hydraulic cam chain tensioner; and sequential multi-port-fuel injection. The multi-function tachometer includes an oil-change reminder system.

We initially tested the Suzuki DF140 in the waters adjacent to Florida's Key Largo on a Wellcraft 180 Sportsman. In use, the original incarnation of this engine delivered strong acceleration, quiet operation and exceptional fuel economy. It is also ran super clean, complying with California's stringent three-star, 2008 standards for outboard engine emissions, as well as the federal Environmental Protection Agency's 2006 outboard emissions standards.

Suzuki DF140 Specifications and Test Results

Test Results

(a)Based on 90% fuel capacity
(b)Optimum cruising speed

Acceleration, 0-30 mph: 8.4 seconds.

Sound Measurements (dBa)

Suzuki DF140A

In 2012 Suzuki revisited the DF140 and introduced the DF140A (along with the DF115A). Based on the same basic model, the engine was tagged with the "A" designation denoting a range of improvements. Foremost among them was the inclusion of a knock sensor, something previously reserved for larger V6 models, and Suzuki's Lean Burn Control feature. The cowl was also redesigned to boost airflow by 45-percent. Overall, Suzuki claimed a fuel efficiency jump of 14 percent, reduced vibration, and more responsive acceleration.

Suzuki DF140B

This engine's latest version hit the water in 2022, when the DF140B was introduced along with the DF115B and the DF100C. While the basics remain the same, compression ratio jumps from 9.7:1 to 10.6:1 for improved acceleration and top speed. Efficiency rose in the neighborhood of 10 percent, and a new air intake design has a silencer-resonator to hush the noise levels and improve water separation. Suzuki also made a number of small-scale changes to help increase longevity, such as using zinc-coated fasteners and optimizing the gear oil passage to lower gear oil temperature for better cooling efficiency, resulting in increased pinion gear durability. Suzuki also made the engine easier to service by incorporating a new oil filter mount accessible by removing only the upper cowl, along with a spill-catcher to reduce the mess.

Now in its third generation, the Suzuki DF140 powerplant has more than proved its value on the marketplace. One of our editors ran a DF140A on a 19' Twin Vee for over five years and 500 hours of use, without ever experiencing a single breakdown or need for service beyond scheduled maintenance. And additional reports of satisfied customers running this 140-hp outboard are not in short supply. This design may be a bit long in the tooth, but that's only because its performance and reliability continue to top the charts.

Editor's Note: This article was last updated in October of 2025.