Detailed Workshop Manual for Yamaha YFM350FWBJ ATV (1997-1999) – 318 Pages | Shop Standards

YAMAHA YFM350FWBJ SERVICE MANUAL

All-terrain performance maintenance for the Big Bear series requires precision-tuned timing and specific torque sequences to survive rigorous off-road utility cycles. Professionals utilize this technical resource to bypass the guesswork of complex 4x4 drivetrain synchronization and carburetor optimization. Eliminating experimental repairs ensures that every planetary gear engagement and top-end overhaul meets factory-spec clearances for maximum mechanical longevity.

Technical Document Inventory

• Total Pages: 318
• Document Number: LIT-11616-10-58
• Publication Era: Late 1990s Revision
• File Format: PDF (High-Resolution Digital)

Operational ROI & Asset Protection

• Preventive maintenance protocols prevent catastrophic transmission failure and secondary gear wear.
• Accurate electrical testing values eliminate the cost of replacing functional CDI or stator components.
• Factory-specified lubrication schedules protect critical internal bearings under heavy-load scenarios.
• Correct valve clearance data ensures optimal engine cooling and prevents premature seat recession.

Active Model & Revision Coverage

This technical repository provides full-coverage data for the Yamaha YFM350FWBJ (1997-1999) Big Bear 350 series. Actionable repair procedures and engineering specifications are explicitly detailed for the primary 4WU series, including regional variants for the USA and Canada (4WU1, 4WU2). The data focuses on the air-cooled, 4-stroke SOHC powerplant and the dual-range 4WD drivetrain configurations specific to these production years.

Logic & Troubleshooting Protocols

Systematic diagnostics focus on isolating starting failures, ignition timing irregularities, and fuel-air ratio imbalances. The manual provides specific resistance values for the pickup coil and source coil to identify electrical bottlenecks. Detailed troubleshooting charts address "No-Start" conditions, mid-range bogging, and 4WD engagement mechanical resistance, ensuring a logical path from symptom to permanent resolution.

Hardware Entity | Technical Target | Maintenance Benefit

| :--- | :--- | :--- | | SOHC Valvetrain | IN: 0.06–0.10 mm / EX: 0.16–0.20 mm | Prevents thermal expansion damage | | Combustion Core | 8.6:1 Compression / 850 kPa | Maintains peak torque and fuel efficiency | | Middle Gear | 0.1–0.3 mm Backlash | Reduces drivetrain vibration and noise | | NGK Spark Gap | 0.6–0.7 mm (DR8EA) | Ensures consistent cold-weather ignition | | A.C. Magneto | 14V / 19A @ 5,000 r/min | Guarantees battery charging under winch load |

System Integration & High-Res Schematics

Technical illustrations include exploded-view diagrams of the constant-mesh 5-speed transmission and the semi-automatic centrifugal clutch assembly. High-definition wiring schematics trace the full path from the C.D.I. unit to the lighting and starting circuits, allowing for infinite zoom on terminal identifiers and wire color codes. Specialized flowcharts detail the hydraulic-mechanical interface of the front differential and rear final drive shafting.

Master Service Chapters

• General Machine Information & Identification
• Technical Specifications & Service Limits
• Periodic Inspection & Lubrication Intervals
• Engine Overhaul (Top & Bottom End)
• Fuel System & Carburetor Calibration
• Drivetrain, Middle Gear, and Final Drive
• Chassis & Suspension Architecture
• Electrical System & Integrated Circuitry

FAQ

How should the centrifugal automatic clutch be calibrated for peak engagement? Clutch performance is governed by both the centrifugal shoe thickness and the manual adjuster setting. Shoes must be replaced if they wear below the 1.5 mm limit to prevent slipping during the 2,950–3,300 r/min stall revolution range. To adjust the release mechanism, loosen the locknut and turn the adjuster counterclockwise until resistance is felt, then back it off exactly 1/8 of a turn to provide the necessary internal clearance for smooth shifting and power transfer under heavy utility loads.

What are the critical lubricant capacities for a full drivetrain service? A comprehensive fluid overhaul requires three distinct types of lubricant to protect the 4x4 architecture of the YFM350FWB series. The engine crankcase requires 2.9 L of SAE 20W40 for a standard change, while the final gear case takes 0.25 L of SAE80 GL-4 hypoid gear oil. The front differential utilizes a specialized gear oil requiring 0.2 L of SAE80W-90 GL-5, ensuring the internal gears remain lubricated to avoid the heat-related pitting common in high-stress field operations.

Which benchmarks indicate a failing electrical charging system? Field diagnostics of the charging circuit require a multimeter to verify a nominal output of 14V at 3,000 r/min. If the battery is not maintaining its charge, check the stator coil resistance across the white-to-white leads, which should read between 0.702 and 0.858 ohms at 68°F. Values outside this window, or a source coil resistance failing to meet the 270–330 ohm spec, indicate internal shorts that will eventually lead to ignition failure and reduced machine uptime.

How do I properly index the timing for a valve clearance check on the 4WU engine? Precision timing is achieved by rotating the crankshaft counterclockwise until the "T" mark on the rotor aligns perfectly with the stationary pointer on the crankcase cover. At this Top Dead Center position, ensure the rocker arms have palpable slack; maintaining the intake gap at 0.06–0.10 mm and the exhaust at 0.16–0.20 mm prevents thermal expansion from holding valves open. This calibration ensures the machine maintains its standard 850 kPa compression pressure for reliable starting.

What is the specific procedure for synchronizing the middle drive gear backlash? Achieving the correct gear lash is critical for shaft drive longevity and involves measuring the play between the middle drive and driven gears, which must stay within the 0.1–0.3 mm range. If the lash exceeds these tolerances, you must adjust the shim thickness behind the bearing housing to re-position the gear engagement. Correct shimming prevents the excessive whining and gear tooth shearing often found in units subjected to constant heavy-duty hauling.