16400-ZY4-A01 Throttle Body Assembly - Overview. The 16400-ZY4-A01 throttle body assembly is a critical component in Honda marine engine systems. It regulates the airflow into the engine, which is essential for controlling engine speed and performance, especially in Honda's active marine engines. Designed to the exact specifications of Honda, it ensures seamless integration with existing parts, maintaining optimal performance and durability.. Key Features. Throttle body assembly that controls ai