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As a result of our researches into reduction of exhaust emissions for small utility two-stroke engines which are widely used for handheld equipment such as a brush cutter and a hedge trimmer, we here discuss how much exhaust emissions can be reduced with only minor modifications of an engine. For the purpose of reducing emissions, we evaluated the effects of exhaust timing retard and of enleanment of carburetor mixture on mass emissions using the existing 25cc two-stroke engine, which emits high levels of HC and CO, and substantially low levels of NOx. We attained great reduction of HC and CO. The power output, however, dropped and both the plug seat and the exhaust gas temperatures rose, which would detract the practicability of the engine. But we solved the problems by modifying the combustion chamber and the exhaust port shape, keeping the emissions reduced as mentioned above.

Today one of the most essential features for engine-powered work machines is that it must be “user friendly”. The recently developed FD590V vertical shaft liquid-cooled 4-stroke V-twin engine is not only a lightweight compact engine, but has improved versatility in many applications of work machines by integrating the entire cooling system with the engine package. The engine is also a high performance, high quality engine designed to provide an improved working environment and easy maintenance. The engine features new technology for a unique liquid-cooled V-twin with excellent operating characteristics. This paper will explain the overall specifications and features of the FD590V, while introducing various technical aspects applied and the results of studies made during the design and development stage.