Frequently Asked Questions

What is Suzuki 4-Stroke Technology?

Suzuki 4-Stroke Technology

Four-stroke engines are clearly the dominate force in marine outboard power. When done right, they're cleaner, quieter, more efficient and more economical than a comparable two-stroke. Over the years, Suzuki has built millions of four-stroke automobile and motorcycle engines, which makes it easy for us to transfer all that proven know-how to an outboard motor. Our commitment to technology means you get better value from our outboards with better fuel economy, improved reliability, and exciting performance. And that is why Suzuki is able to offer the most advanced four-stroke outboard motors on the market today.

The Evolution Continues

What do we mean by "most advanced"? Well, our digital sequential fuel injection reduces fuel consumption by 75% compared to an equal displacement two-stroke, and by 30% when compared to competitive four-stroke outboards. Suzuki's fully-transistorized direct ignition, the first in outboard power, ensures first-time starts and maximum power, and helps prevent misfires. The tuned intake manifold boosts low- to mid-range performance for quicker acceleration. The cooling system uses a thermostat to maintain optimum operating temperature for maximum engine efficiency.

You'll find similar combinations of proven automotive and marine technologies in our new portable DF30/25 models and portable 15 and 9.9 horsepower four-strokes as well.

And every Suzuki four-stroke already meets applicable EPA emissions standards for the 2006 model year. Every Suzuki Outboard has also earned the California Air Resources Board (CARB) 3 Star Ultra Low Emissions Rating.

A Closer Look

No one else can match the engineering found on Suzuki Outboard engines. And here's why:

  • The DF25 is unique in the fact that it utilizes a single-cam, 3-valve head design (two intake valves, one exhaust valve). This design, when used in combination with a 538cc displacement (with a bore and stroke of 71mm x 68mm), provides greater output and low-end torque, resulting in outboards that are easier to handle, even at lower speeds.
  • 25_30CYLRHD.1923.05.jpgAn in-line, three-cylinder, automotive-type engine was utilized in the design of the DF50/40 Suzuki. Components such as valves, valve springs, tappets, sprockets, timing chain and fuel filter are all identical to those used in Suzuki automotive engines. Because of the different operating conditions and environment, however, the engines have been given a larger bore and longer stroke to provide maximum power in a marine application. Critical structural parts have been redesigned for marine use, such as the cylinder head, block, crankshaft, connecting rods, camshafts and pistons, to provide maximum reliability and durable operation. Metal gaskets have also been employed in critical areas.
  • cutaway.gifThe DF50/40, on the other hand, uses a Dual Over Head Camshaft (DOHC) cylinder head, featuring four valves for each cylinder. This compact, modern head utilizes a Pent Roof design, which allows for closer placement of the intake and exhaust valves, helping to optimize combustion efficiency. A center-positioned spark plug and high-compression ratio are also incorporated to maximize engine performance.
  • The DF50/40 were the first outboard motors to be equipped with an enclosed, oil-bathed timing chain, which is kept in check with an automatic hydraulic tensioner. Highly durable, the system will provide owners with years of maintenance-free operation.
  • timingchn.gifA crankshaft-driven lubrication system with a trochoid type oil pump is used in all of Suzuki's bigger four-strokes. With the inclusion of a cartridge type oil filter, the durability of the crank journal and big end have been greatly improved. The oil drain is positioned on the front side of the engine, making oil changes easier, and allows for easy servicing in the full tilt position.
  • The long-track intake manifolds utilized on Suzuki's DF40-70 models are made of a special corrosion-resistant plastic, and are designed to increase the velocity of the fuel-air mix for more power and quieter operation. In addition, this style of air intake system reduces changes in air temperature and helps to increase power, as well as acting as a large-volume silencer to reduce engine noise levels.
  • The solid-state ignition system found on the DF40-70 models provide twice as much power to the spark plug, allowing for cleaner, more complete combustion, maximizing power with every stroke.
  • The Digital CDI utilized on the DF4, 6, and 25 provides precise control of engine performance. Sensors providing engine rpm and temperature data in real-time allow the unit's computer to instantly determine optimum engine timing. The results are smooth operation at low speed, powerful acceleration, and stable operation at high speed.
  • sparkplg.gifThe DF40, 50, 150, 175, 200, 225, 250, 250SS and 300 features a "direct ignition" system, which is more compact and simpler in design because it uses fewer parts than conventional ignition systems. The ignition coils are integrated within the spark plug caps, simplifying the wiring system and greatly reducing electronic engine "noise," which can interfere with VHF radios, fishfinders and other marine electronics.
  • Suzuki High output alternators will keep your electronics humming.
  • An advanced computer diagnostic system allows dealership technicians to quickly troubleshoot the DF40-300 models, thus reducing diagnostic time.
The Heart of the Matter

One of the most important features found on the Suzuki DF40-300 models is the Sequential Multi-Point Digital EFI system. Improved fuel economy and optimum power are achieved through the constant monitoring of engine and operating conditions by way of highly-advanced computer-control. With this particular electronic fuel injection system these outboards are able to pass future emission regulations today while providing lower fuel consumption, easier starting, better drivability and outstanding throttle response.

The E.C.M. (Engine Control Module) system incorporated into these models controls the engines' ignition system and also 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 M.A.P. (Manifold Absolute Pressure), Engine RPM Sensor, Air Intake Temperature Sensor, Exhaust Manifold Temperature Sensor and Cylinder Wall Temperature Sensor. The data from these sensors is conveyed to a computer which instantly calculates (Speed-Density type) the optimum amount of fuel to be injected at high pressure into each of the cylinders.


Also incorporated on these models are the Idle Air Control, a Fast Idle function and a Dash Pot System to provide stable engine operation at all times. The I.A.C. is programmed to let the engine idle at a low rpm. Regulating intake air under different running conditions, intake air is increased when the engine's rpm is too low, and decreased when rpm is too high.

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

Suzuki's Dash Pot System is of an electronic type; 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 to lessen stress on the engine.

Although common in automotive applications, Suzuki was the first to incorporate a Solid State Full Transistor Digital Ignition System into an outboard engine application. This system taps into voltage supplied by the battery, enabling it to increase spark duration regardless of engine speed—a nine-fold increase compared to spark duration produced by conventional CDI units. The result is a doubling of spark strength. Compared to conventional CDI units, it is controlled with only 1/10th the voltage. The circuit design is simplified and creates more energy and a longer fuel burn, therefore increasing durability and reliability.

The Bottom Line

No other outboard manufacturer has more knowledge about engines than Suzuki. We've been building engines for automobiles, motorcycles and outboards for decades. Our technical resources are enormous. Suzuki is the largest corporation manufacturing a full line of outboard motors. We know the technology inside and out; we know it works. Our innovation is based on experience and good old fashioned know how.