1999 Yamaha Big Bear 400 ATV Service Manual with 2WD & 4WD Supplements (P/N LIT-11616-13-22)

This Yamaha Big Bear 400 service manual combines the June 1999 base publication LIT-11616-13-22 for YFM400FWNM/YFM400FWNMC (5FU1/5FU2) with supplements LIT-11616-13-34 for YFM400NM/YFM400NMC (5GW1/5GW2) and LIT-11616-15-22 for YFM400FWNP (5FUA). Both supplements are used with the included base manual.

• Engine overhaul: Engine removal, cylinder-head and valve work, piston and crankshaft inspection, balancer service, timing-chain installation, and reassembly.

• Clutch and transmission: Primary and secondary clutch inspection, shift-fork and gear checks, middle drive shaft service, and recoil starter repair.

• Carburetion: Mikuni BSR33 teardown, jet and diaphragm inspection, float-height and fuel-level adjustment, plus separate California carburetor specifications.

• Drivetrain: Differential gear case and constant velocity (CV) joint service, rear axle and final drive repairs, shim selection, and gear-lash measurement.

• Brakes and chassis: Hydraulic brake bleeding, caliper and master-cylinder repair, rear drum service, steering knuckle and tie-rod inspection, and swingarm bearing replacement.

• Electrical diagnosis: Wiring schematics and troubleshooting flowcharts for ignition, starting, charging, lighting, cooling-fan control, carburetor warming, and the FWNP 2WD/4WD selector.

Written primarily for Yamaha dealers and qualified mechanics, the manual assumes familiarity with mechanical principles and workshop repair procedures.

Engine and Carburetor Repair

Engine overhaul coverage extends to valve-guide replacement and reaming, valve-seat lapping, piston-to-cylinder measurements, and crankshaft inspection. Lubrication diagrams trace the oil pump, oil cooler, crankshaft, and transmission oil paths.

The carburetor section covers the coasting enricher and vacuum piston, with float-height adjustment views and fuel-level measurement using gauge YM-01312-A / 90890-01312. The base specifications distinguish the standard and California jet-needle configurations.

Gear Setup and Variant-Specific Procedures

Middle-gear and final-drive shim calculations use markings on the gears, crankcase, and bearing housings. The measurement views and shim tables help select the correct setup after replacing a gear or housing.

The base-model limited-slip differential is factory assembled. Its service coverage includes removal, inspection, and gear-lash adjustment, but Yamaha warns against dismantling the internal differential unit because this can cause malfunction.

The 2WD supplement revises engine removal, middle-gear service, and front-wheel removal. The FWNP supplement adds gear-motor installation, the shift fork sliding gear and 2WD/4WD shift sleeve, and a separate differential-lash procedure using tool YM-01467 / 90890-01467.

The gear-lash procedures also identify a specific damage risk: overtightening the ring-gear holding bolt can damage the ring gear.

Chassis Repair and Electrical Fault Tracing

The steering section includes ball-joint replacement using YM-01474 with attachment set YM-01477, plus front wheel-bearing service. Cable-routing and shift-pedal adjustment views support reassembly.

Electrical diagnosis follows no-spark, no-crank, charging, and lighting faults through connector tests and pass/fail branches. The FWNP supplement adds separate checks for the On-command switch, gear motor, and four-wheel-drive indicator.

For brake, axle, and swingarm work, follow the manual's support and safety precautions and standard shop safety practices.

A Preview of Fastener Torques and Pickup-Coil Data

These are a few of the workshop values included in the manual.

The YFM400FWN base manual specifies 140 Nm for the primary-clutch carrier nut and 23 Nm for the final gear case oil filler bolt.

The pickup-coil test specification is 459–561 ohms at 20°C (68°F) in both the base manual and FWNP supplement. The ignition troubleshooting sections identify the White/Green and White/Red leads used for this check.

PDF Navigation and Included Publications

Search, bookmarks, and wiring detail: The main manual and FWNP supplement have searchable text; the 2WD supplement does not. Some main-manual flowcharts also lack searchable text. Embedded bookmarks open the main chapters, base wiring diagram, and both supplements. Small wiring labels require magnification.

One printable 425-page PDF contains the 339-page base manual, 35-page 2WD supplement, and 51-page FWNP supplement. These totals already include the 25 cover, introductory, and contents pages across the three publications, together with the wiring diagrams.