The 1985 Suzuki GSX-R400, model code GK71B, represents an early and significant entry in Suzuki's renowned GSX-R sportbike lineage. This liquid-cooled, inline-four motorcycle, powered by a 398 cc engine, was engineered for performance and agility, reflecting the burgeoning supersport segment of the mid-1980s. Its design emphasized a lightweight, race-inspired philosophy, a hallmark that would define the GSX-R series for decades to come. The GK71B offered an approximate 58-60 horsepower, making it a potent machine for its era, aimed at enthusiast riders seeking a blend of track-ready capabilities and street usability. This comprehensive service repair manual is designed to be the definitive guide for maintaining and repairing the 1985 Suzuki GSX-R400 GK71B. It covers all essential aspects of the motorcycle, including detailed procedures for engine systems, fuel delivery, chassis components, and the electrical system. From routine maintenance tasks like oil changes and chain adjustments to in-depth repair procedures such as engine overhauls and carburetor rebuilds, this manual provides clear, step-by-step instructions. It also includes crucial troubleshooting guides and technical specifications, empowering owners, mechanics, and technicians to keep this classic sportbike in optimal condition.