This manual covers the GPZ400 and GPZ550 models produced between 1979 and 1985. These motorcycles are celebrated for their inline-four, DOHC, air-cooled engines, offering robust performance for their time. The GPz line represents a commitment to sportbike evolution, incorporating advancements in chassis design and engine technology. With a history rooted in performance, these models were well-regarded for their handling and contributed significantly to the reputation in the sportbike segment. This comprehensive workshop service repair manual provides professional-level information for the maintenance and repair of all GPZ400 and GPZ550 models. It includes detailed procedures for engine top-end work, lubrication, fuel and cooling systems, clutch and transmission, wheels, brakes, suspension, steering, and electrical systems. The manual offers step-by-step instructions for disassembly, assembly, cleaning, and reinstallation, along with troubleshooting guides and technical specifications. This resource is designed to assist owners, independent repair shops, and DIY enthusiasts in keeping their motorcycles in optimal condition.