This workshop service repair manual covers the Mongoose/KXR 90/50 All-Terrain Vehicles. These ATVs, manufactured by a Taiwanese powersports company, are designed as entry-level and youth models. They typically feature a 2-stroke, air-cooled, single-cylinder engine with a carburetor and CDI ignition, paired with an automatic CVT transmission and chain drive. Known for their value proposition in the powersports market, these ATVs offer a robust steel tube frame and essential features like headlights and taillights for visibility, along with safety considerations such as a throttle limiter. This comprehensive English-language manual provides complete factory service and repair information, intended for both do-it-yourself owners and experienced mechanics. It delves into detailed step-by-step instructions, supported by hundreds of photos and illustrations, covering all major systems including engine overhaul, transmission, electrical systems, chassis, suspension, and braking systems. The manual also details routine maintenance procedures, repair processes, troubleshooting, and diagnostics, enabling users to effectively maintain and repair their Mongoose/KXR 90/50 ATVs, ensuring optimal performance and longevity.