Development of a Small Motorcycle EFI Retrofit System

Carbureted small displacement motorcycles are the most common form of road transport in Asia. Small displacement motorcycles have historically been low-cost and low-tech. In order to achieve the best overall performance, economy and emissions, a more sophisticated fuel injection system is required. To address the fuel consumption and emissions of existing “legacy” vehicles, we have developed an Electronic Fuel Injection (EFI) retrofit for common small motorcycles in Asia. The system leverages existing components as much as possible allowing focus on integration into the host vehicle and overall system tuning. This paper details the overall system design, modeling, component selection and system tuning of a 120 cc single cylinder four stroke EFI retrofit kit. The target vehicle is tested on dynamometer with stock carburetor settings, and with the EFI kit. The EFI system reduces fuel consumption by approximately 10%, HC emissions by 55%, CO emissions by 96% while doubling the NOx emissions and matching the carbureted system's power.