This manual covers the YFZ450R and YFZ450RY models manufactured between 2004 and 2013, primarily focusing on the first generation of these carbureted all-terrain vehicles, with relevant references to later fuel-injected versions. Engineered for performance and durability, these models feature a robust 4-stroke, single-cylinder, liquid-cooled 449cc engine with a DOHC configuration and a 5-speed transmission. The chassis is built with a steel frame, independent double wishbone front suspension, and a swingarm rear suspension, complemented by dual hydraulic disc brakes at the front and a hydraulic disc brake at the rear, making them suitable for demanding off-road applications. This comprehensive service manual provides detailed guidance for the maintenance, repair, and troubleshooting of your YFZ450R/YFZ450RY. It includes step-by-step repair procedures with sub-steps, notes, cautions, and warnings, supported by detailed illustrations, drawings, and photos. You will find information on electrical diagnostics, troubleshooting, technical specifications, and maintenance schedules, including fluid capacities and recommended service intervals. This manual is an essential resource for owners, mechanics, and technicians to ensure the optimal performance and longevity of their vehicle.