Honda TRX400EX Fourtrax 1999–2004 Service Manual (P/N 61HN100)

• Official OEM publication (P/N 61HN100) covering the 397cc single-cylinder dry-sump engine.
• Features 47 exploded-view diagrams and 14 technical torque-value tables for frame, engine, and electrical sub-assemblies.
• Includes specific decompressor assembly details and high-altitude carburetor tuning parameters frequently omitted from standard owner literature.

Structural and Maintenance Scope

This factory service manual provides complete reference material for the major vehicle systems of the Fourtrax. It starts with VIN, engine, and frame serial number locations before moving into comprehensive teardown and assembly breakdowns. Detailed sections document the cylinder head, valve train, cylinder and piston assemblies, clutch, gearshift linkages, and alternator components. You will also find electrical schematics covering the ignition, charging, and lighting systems.

Additional chapters cover the lubrication system, detailing oil pump inspections and strainer maintenance protocols. The fuel section breaks down the carburetor configuration, including jetting specs for both standard and high-altitude riding conditions. For the chassis, the manual outlines wheel, suspension, and steering system care. If you are curious about the general structure of factory materials, you can read more about what an OEM service publication covers for long-term vehicle maintenance.

Technical Preview and Reference Values

This publication lists specific clearances and capacities for the 397cc powerplant. For example, intake valve clearance is set at 0.10 mm (0.004 in), while the exhaust valve clearance is specified at 0.12 mm (0.005 in). Engine oil capacity is documented at 1.8 liters after draining. The carburetor uses a #148 main jet as the standard factory setting for low-altitude operation, and piston-to-cylinder clearance falls within the standard 0.015–0.050 mm range. Essential torque values are fully documented, including 44 N-m for cylinder head nuts and 108 N-m for the clutch center lock nut.

Working on ATVs involves inherent mechanical risks. Proper maintenance requires a safe, well-ventilated workspace, and anyone attempting extensive engine work should follow standard shop safety practices or consult a certified mechanic.