1999–2004 Honda TRX400EX Fourtrax ATV Service Manual (P/N 61HN105)

This Honda factory service manual covers maintenance, troubleshooting, and repair of the 1999–2004 TRX400EX Fourtrax, including its engine, drivetrain, chassis, and electrical systems.

Supplied as one 265-page PDF in English.

• Engine repair: Engine removal and installation, cylinder-head and valve-train service, decompressor overhaul, cylinder and piston inspection, and camshaft installation.

• Clutch and transmission: Wet-clutch service, gearshift linkage repair, crankcase separation, transmission rebuilding, and crankshaft/balancer inspection and installation.

• Fuel and lubrication: QB10A carburetor overhaul, pilot-screw and high-altitude adjustment, oil-pump inspection, strainer cleaning, and oil-cooler service.

• Suspension and steering: Wheel-hub service, suspension-arm inspection, steering-shaft and tie-rod repair, rear-axle bearing replacement, swingarm pivots, and shock linkage.

• Hydraulic disc brakes: Front and rear master-cylinder and caliper rebuilding, pad/disc inspection, fluid replacement, air bleeding, and parking-brake adjustment.

• Electrical troubleshooting: Charging and ignition tests, electric-starter repair, switch checks, wiring diagrams, cable and harness routing, and fault-finding charts.

This manual suits mechanics familiar with standard workshop procedures and equipped for component measurement, electrical testing, and press work.

Engine, Clutch, and Transmission Repair

Top-end coverage extends to cylinder-compression testing, valve-guide replacement, valve-seat inspection/refacing, and cam-chain tensioner checks. Valve-seat cutter views and component wear limits support inspection before reassembly. Symptom charts also cover hard starting, low power, poor idle, and handling complaints.

The manual distinguishes work that can be done with the engine in the frame from transmission and crankshaft/balancer work requiring engine removal. Transmission exploded views identify the mainshaft and countershaft assemblies, shift forks, thrust washers, and snap-ring orientation.

The decompressor section covers its one-way clutch and reverse decompressor cam; its press-work cautions address the risk of cracking the cam-sprocket flange. Separate valve-clearance notes explain how decompressor operation can affect measurements.

Factory tool references identify the clutch center holder (07724-0050002) and rotor puller (07733-0020001), plus the U.S. rotor-puller alternative (07933-3950000). Component-specific torque tables, oil capacities, valve and piston clearances, and wear limits accompany the procedures.

QB10A Carburetor and Dry-Sump Lubrication

Carburetor procedures cover the accelerator pump, air cut-off valve, float inspection, and piston/butterfly throttle synchronization. Float-pin instructions distinguish 1999–2000 models from later versions, alongside separate pilot-screw idle-drop and high-altitude adjustment procedures.

The lubrication chapter covers relief-valve checks, pump-rotor inspection, crankcase and oil-tank strainers, and oil-cooler/tank removal. Its oil-filter warning identifies reversed installation as a cause of severe engine damage.

The crankcase emission-control diagram shows the breather storage tank and its connection to the intake. Model-identification illustrations locate the VIN, frame and engine serial numbers, and carburetor identification number.

Chassis and Brake Service

Front-end repair includes wheel-bearing replacement, suspension-arm spherical bearings, tie-rod assembly, and toe adjustment. Rear suspension coverage reaches the axle bearing holder, shock-linkage needle bearings, swingarm bushings, and shock-absorber mounting bearings.

The rear-axle section distinguishes actual lock-nut torque from the torque-wrench reading when using the specified extension tools. Brake coverage includes master-piston inspection, caliper seals, and the rear caliper's cable-operated parking-brake mechanism.

Shock-absorber coverage is limited to removal, inspection, mounting-bearing work, and installation; internal damper rebuilding is not included.

Follow the manual's precautions for hydraulic brake work and the nitrogen-charged rear shock, and use a well-ventilated workspace.

Electrical Tests and Fault Isolation

Peak-voltage tests cover the ignition coil, exciter coil, and ignition pulse generator, with connector-level checks for the ICM. Comparing readings at the component and module connectors helps distinguish wiring faults from a faulty source component.

Charging-system and electric-starter troubleshooting charts accompany the wiring diagram, switch-continuity tables, and cable/harness routing illustrations. Starter-motor brush and armature inspection, starter-relay testing, and clutch-diode checks extend coverage beyond replacing electrical assemblies.

Lighting and switch sections cover the headlight, taillight, neutral indicator, ignition switch, and handlebar switches.

PDF Search, Bookmarks, and Diagram Detail

The total includes one cover page, three introductory pages, five memo pages, and the two-page index. Bookmarks link to the contents and all 21 sections; OCR supports searches across the main text, although recognition errors can affect matches and the cover and full wiring diagram are not searchable. Small wiring labels require zooming for comfortable reading.