Yamaha YFM400FWNP ATV Service Manual Set, 2000–2006 (P/N LIT-11616-15-22)

Both supplements require the included base manual for complete service procedures. The FWNP supplement covers the selectable 2WD/4WD system and revised specifications; the NM/NMC supplement provides the changes for the 2WD models.

PDF Search, Bookmarks and Wiring Detail

Text access and diagram detail: Only the opening FWNP supplement has searchable PDF text. Embedded bookmarks provide access to all three publications and their main sections. Small wiring labels require zooming; the shaded circuit pages in the base manual have lower contrast.

One printable, 427-page PDF in English contains all three publications. The page totals include the covers, introductory and contents pages, rear cover, and two full wiring-diagram sheets.

Engine Overhaul, Shaft Drive and Circuit Diagnosis

The following selected service topics show the main repair areas. Other included work covers spark arrester cleaning and headlight beam adjustment.

• Engine repair: Step-by-step procedures for engine removal, crankcase separation, cylinder-head service, piston inspection, timing-chain replacement and engine reassembly.

• Clutch and transmission: Primary and secondary clutch inspection, shift-fork and gear checks, transmission assembly and clutch adjustment.

• Carburetion and maintenance: Mikuni BSR33 carburetor disassembly and fuel-level adjustment, valve-clearance inspection, compression testing and oil-service procedures.

• Shaft drive: Constant velocity joint service, differential assembly, middle-gear and final-drive shim selection, gear lash measurement and gear-motor installation.

• Brakes and chassis: Hydraulic brake bleeding, caliper and master-cylinder service, rear drum brake repair, steering-knuckle work and double-wishbone suspension inspection.

• Electrical troubleshooting: CDI ignition, electric starting, charging, lighting, signal, fan and carburetor-warming circuits, plus the FWNP 2WD/4WD selecting system.

Written primarily for Yamaha dealers and qualified mechanics, these manuals assume an understanding of mechanical concepts and machine repair procedures.

Engine Internals and Valve Timing

The overhaul chapter goes beyond removal and installation. It covers valve-guide replacement, valve-seat inspection and lapping, cylinder and piston measurements, crankshaft inspection, and oil-pump clearances.

Lubrication diagrams and valve dimension views accompany the inspection data. Having the factory limits beside the repair procedures lets you compare component measurements before selecting replacement parts.

Recoil starter service includes the rope, sheave drum, pawls and spring. Transmission inspection addresses gear engagement, shaft runout and shift-fork movement, with assembly illustrations for the internal components.

Mikuni Carburetor Identification and Adjustment

The carburetor chapter covers the needle valve and seat, jets, piston valve and coasting-enricher diaphragm. Float-height and fuel-level checks are supported by measurement illustrations.

The FWNP supplement identifies carburetor calibration 5FUA 12; the base specifications distinguish the 5FU1 and California 5FU2 calibrations. This distinction matters when matching the carburetor data to the machine.

Differential, Middle Gear and Final Drive

Middle-gear and final-drive sections explain shim selection using component markings, with gear lash measurement charts and thrust-clearance checks. The FWNP supplement provides a separate differential setup procedure and gear-motor alignment requirements.

The base manual prohibits disassembly of its factory-assembled internal differential unit. Its surrounding service procedures cover bearings, seals, lash adjustment and constant velocity joints.

The differential lash procedure warns that overtightening the temporary ring-gear holding bolt can damage the ring gear.

Steering, Wheel Bearings and Suspension

Steering service includes ball-joint replacement using the specified remover/installer and front wheel bearing installation. Front-arm bushing checks and swingarm pivot-bearing inspection extend the chassis coverage beyond routine adjustments.

Brake chapters include component inspection criteria, seal replacement requirements and hose-routing information.

Electrical Tests and Fault Isolation

Starting circuit operation schematics explain the relationship between the starter, relays, brake switch and gear-position switch. Diagnostic charts connect continuity, resistance and voltage checks to named components, helping narrow electrical faults before replacement parts are selected.

Cable routing diagrams show harness, hose and control-cable placement. Full wiring diagrams accompany the base manual and FWNP supplement.

Follow the manual’s precautions for live electrical testing and supporting the ATV during service.

Preview of Ignition-Coil and Differential Specifications

For the YFM400FWNP, ignition-coil primary resistance is 0.18–0.28 Ω and secondary resistance is 6.32–9.48 kΩ, both at 20 °C (68 °F). The troubleshooting section identifies the corresponding test connections.

The FWNP differential gear lash specification is 0.09–0.47 mm (0.004–0.019 in). Its measurement and shim-selection information applies to the supplemented differential configuration.