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Suzuki’s four-stroke outboards, the DF115 and DF140, are the product of years of experience in the design, development and manufacturing of motorcycle, automotive and outboard engines. Experience that has resulted in environmentally friendly, award winning designs. 

Suzuki engineers have gone to great lengths to keep both engines as compact as possible. The utilization of an offset drive shaft, combined with a two-stage mixed cam drive—a first for any outboard—offers overall compactness as well as increased performance. Suzuki engineers also worked hard to make these outboards as quiet as possible. A larger silencer, a very low 620 rpm idle speed and stiffer crankshaft, crankcase, engine holder and cowling all work together to reduce engine noise and vibration. 

Performance is delivered with the engine’s superior power and enhanced prop efficiency due to the use of a 2.59 gear ratio, large pitch and diameter prop. 

These motors not only meet the 2006 EPA* exhaust emission standards, their clean, efficient operation has allowed them to comply with the 2008 CARB** which represents a 65% reduction from the 2006 EPA emission standards. 

Committed to the future, Suzuki has and will continue to provide boaters with the best in performance, reliability and durability it has to offer. 

Compact Outboards 

Along with creating clean-running outboards, another important goal that Suzuki engineers set for the DF series was to create a compact outboard. With the DF115 and DF140 they have surpassed their goal. The overall design has the same sleek, flowing lines that have been found throughout the entire DF series. 

But it is underneath the body where Suzuki’s engineers have been hard at work. In order to create a compact outboard, they incorporated an offset drive shaft into the system. The use of the offset drive shaft allowed for other size-reducing measures such as the utilization of two-stage mixed cam system, which in turn has allowed the use of a smaller cam sprocket, smaller cylinder head and cover. 

After so much size reduction, what’s left are two outboards that are compact yet deliver the power and performance users demand. 

Suzuki’s Advanced Engineering 

A long history in the design and manufacture of motorcycle, automotive and marine engines gives Suzuki an unrivaled ability to blend the best of its advanced technology and know-how into the creation of the D115 and DF140 outboard engines. Based on proven automotive designs, engines for both outboards have been specifically redesigned for use in marine applications. 

The DOHC, 4-valve cylinder head is designed to keep overall size to a minimum. The engineers utilized an offset drive shaft system with a reduction gear incorporated at the bottom of the power head to transfer power from the crankshaft to the drive shaft. 

The utilization of a two-stage mixed cam drive system, the first time this system has been used in outboards, incorporates both gears and a chain. The first stage gears transfer power between the crankshaft and the drive shaft while the second stage utilizes a chain to deliver power from the drive shaft to the camshaft. 

As gear reduction allows for the use of a smaller diameter cam sprocket as well as a smaller cylinder head and cylinder head cover, the greatest merit of this system is the significant reduction in the overall size of the engine. Valve angles are also reduced to offer a more compact combustion chamber for increased combustion efficiency. 

The Cam Drive System utilizes a highly durable timing chain. The timing chain is equipped with an automatic hydraulic tensioner to keep the chain properly tensioned. The system will provide users with years of maintenance-free operation. 

Both models also feature a two-stage reduction gear that delivers a larger gear ratio of 2.59. On the drive shaft, the first stage reduction delivers a ratio of 1.25 while the second stage, in the gear case itself, delivers a further reduction of 2.08. The biggest gain this system delivers is in its capability to use a highly efficient, large pitch, large diameter propeller. 

A group exhaust system utilized in the cylinder head and cylinder block increases power output by reducing drag in the exhaust system with better exhaust flow through its 4-2-1 design. 

Compared to previous outboards, the offset drive shaft system puts the center of gravity closer to the front of the outboard allowing the upper mount to be positioned above the torque roll. Also, increasing the mounts capacity—by 1.8 times on the upper mount and 1.6 times on the lower compared to our 2-stroke V6 outboards—has led to an effective reduction in engine vibration. 

Fuel Delivery System 

The DF115 and DF140 use a high-volume diaphragm type fuel pump that runs off the cam drive. Upstream of the pressure regulator, a Fuel Cooler is incorporated in place of a water jacket to cool the fuel. All fuel-related components are located on the intake manifold. 

Intake Manifold 

The aluminum-cast intake manifold is designed with a comparatively long branch to boost the engine’s mid range torque. The intake manifold consists of the IAC (Idle Air Control), a Fuel Cooler, Vapor Separator, two types of Fuel Filters, the Throttle Body and related fuel system components. The entire system is assembled into a compact, easy to maintain module. 

The ventilation system is designed to force air from within the upper cover to the outside. Fan blades on the magneto flywheel ventilate air out through the mag cover and upper cover reducing the air temperature within the engine cover. This provides a cooler intake air temperature, which in turn improves engine performance while enhancing reliability and durability of the outboard’s electronics, etc. and keeps air temperature under control. 

Fresh air is channeled through intake ducts to the silencer. The large capacity silencer is equipped with a baffle plate inside for further noise reduction. 

Outstanding Fuel Efficiency 

The graph shows a comparison in the performance of the DF115 engine with the 2-stroke DT115S. At idle, fuel consumption of the DF115 is 75% less than the DT115S. Even at maximum performance levels, the DF115 consumes over 31% less fuel than its 2-stroke counterpart. A relatively flat torque curve also provides plenty of power throughout the entire speed range from low to high speeds and increases its overall drivability. 

When comparing the DF140 4-stroke vs. the DT140 2-stroke, the fuel consumption follows the same line. At idle, fuel consumption of the DF140 is 60% less than the DT140. Even when comparing at WOT, the DF140 consumes over 30% less fuel than its 2-stroke counterpart. The DF140 has a great hole shot to get a boat up on plane quickly. And with a wide power band, the 4 stroke 140 is 2 seconds faster 0-30 mph than the 2-stroke. 

Multi Point Sequential Electronic Fuel Injection 

The DF115 and DF140 both utilize the same Multi Point Sequential Electronic Fuel Injection of the Speed Density type that is found in the every Suzuki 4-stroke fuel injected model. The use of this system enables these outboards to pass future emission standards while providing lower fuel consumption, smoother starting, stable idling, better drivability and outstanding throttle response. 

The E.C.M. (Engine Control Module) system controls the engine’s ignition system and provides an ideal fuel supply under all running conditions. The E.C.M. constantly monitors crucial data, in real time, from a series of sensors placed in critical areas in the engine. The sensor system is made up of the Manifold Absolute Pressure Sensor, Crankshaft Position Sensor, Intake Air Temperature Sensor, Cylinder Wall Temp Sensor, Camshaft Position Sensor, and Exhaust Jacket Temp Sensor. The data from these sensors is conveyed to a computer that instantly calculates (Speed-Density type) the optimum amount of fuel to be injected at high pressure into each of the cylinders. 

The DF115 and DF140 also incorporate an IAC (Idle Air Control) which consists of an Idle Speed Control, Fast Idle Function, and a Dash Pot System to further enhance engine performance with stable operation at all times. 

The Idle Speed Control uses a linear solenoid system and is programmed to let the engine idle at a very low 620 rpm’s. Regulating intake air under different running conditions, intake air is increased when the engine’s rpm’s are low, and decreased when rpm’s are high. 

A Fast Idle Function provides smooth, quick starts and stable engine warm-ups. When the engine is started, the IAC valve fully opens to let an increased flow of air into the cylinder. 

Suzuki’s Dash Pot System is electronic. Other manufacturers generally use mechanical systems. The Electronic Dash Pot System only functions when there is a sudden throttle transition from open to closed, smoothly reducing rpm’s to lessen stress on the engine. 

Blow-by gas generated inside the crankcase is separated into liquid and gas components inside the breather chamber. Only the resulting gas component is sent via the breather hose to the silencer. After this, it is mixed with fresh air, and the resulting mixture is drawn into the combustion chamber and burnt instead of being released as pollution into the atmosphere. 

High Output Alternator 

Both the DF115 and DF140 are equipped with high output alternators that deliver a total of 40A (12V) for increased electrical power. Fan blades incorporated on the large diameter flywheel magneto circulate air out of the engine cover to reduce air temperature. A watercooled regulator makes use of a large capacity power generator. 

Also the DF115 and DF140 are the first Suzuki outboards to utilize a 1.4kw dust-proof starter motor. 

Distinctive Styling With Easy Engine Access for Maintenance 

The distinctive styling found throughout Suzuki’s DF series is evident in the DF115 and DF140 as well. Smooth, flowing lines present a refined image that promotes their clean running characteristics. The lower covers are held in place with fasteners at three locations, one in front and the other two on either side at the rear of the engine. The lower cover separates into two sections, the port and starboard, to allow easier access to the 4-stroke engine. 

Oil changes are easy with the drain plug located on the front of the oil pan making draining of the oil possible with the engine in the tilt up position. A spin on oil filter is utilized and the oil filler cap is attached to the top of the cylinder head to provide easy access from the boat. 

The water pressure valve is attached to the oil pan with its cover attached from the exterior of the oil pan for easy cleaning and replacement without having to remove the power head. 

Keeping the Outboard Cool 

The DF140 utilizes a comprehensive cooling system that circulates water not only through the block but also cools the crankcase, intake manifold, fuel line and a specially designed oil cooler (see above). Its compact and simple design is efficient at keeping oil temperature under control while providing ease of maintenance. 

Multi-Function Tachometer 

The DF115 and DF140 are designed to operate with a Multi-Function Tachometer that includes a comprehensive monitoring system to provide you with an excellent backup to the performance of the outboard engine. Using data supplied from each sensor to the E.C.M., this system detects abnormalities in the running of the outboard, giving you the needed information and alerts before problems arise, so that appropriate measures can be taken before the problem becomes serious.

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