Modification of Two-Stroke Engine Intake System for Improvements of Fuel Consumption and Performance through the Yamaha Energy Induction System (YEIS)

The recent trend of two-stroke gasoline engines indicates that engine power has been ever-increasing. With this trend, new problems have often arisen; that is, there is an area where both engine performance and fuel economy become worse at part-throttle operation. This phenomenon is called the “trough of torque”, and a solution of these problems has been one of the major subjects of two-stroke engine research and development.

This literature discusses the Yamaha Energy Induction System (YEIS), a simple modification of the intake system that has successfully eliminated the trough of torque; thus both engine performance and fuel economy have been greatly improved.

It also discusses the construction and operation of the YEIS, as well as its effect on engine performance and fuel consumption. A large space of this literature is dedicated to the elucidation of the YEIS and the confirmation of improved fuel economy through the mode operation of the YEIS engine.