This manual covers the Mongoose and KXR 90/50 all-terrain vehicles, including models designated by manufacturer codes LA20AB and LA10BA. These ATVs are designed for recreational trail riding and are powered by air-cooled, single-cylinder engines with displacements of approximately 85-90cc for the 90cc models and 49cc for the 50cc models. They feature a Continuously Variable Transmission (CVT) with an automatic clutch and typically utilize hydraulic disc brakes for reliable stopping power. The Mongoose and KXR lines represent a commitment to providing accessible and enjoyable off-road experiences for younger riders and enthusiasts. This comprehensive service repair manual provides detailed information essential for the maintenance and repair of your Mongoose/KXR 90/50. It covers a wide array of systems, including the lubrication, fuel, engine, drivetrain, chassis, and electrical systems. You will find step-by-step procedures for disassembly, assembly, component overhaul, and diagnostics, along with critical maintenance schedules and technical specifications. This manual is an indispensable resource for owners, DIY mechanics, and professional technicians seeking to ensure the optimal performance and longevity of their ATV.