Category:
High-performance motocross/off-road competition motorcycle
Competitors:
Honda CR480R/CRF450, Kawasaki KX450, Suzuki RM465/RM-Z450
Engine Type:
Liquid-cooled, 4-stroke, DOHC, single-cylinder
Performance Focus:
Class-leading power and torque delivery for its era, agile handling.
Target Audience:
Motocross racers, off-road enthusiasts, mechanics specializing in performance dirt bikes.
Engine:
Complete disassembly, assembly, inspection, repair, tuning, troubleshooting
Fuel System:
Carburetor tuning, disassembly, cleaning, repair, fuel pump inspection
Ignition System:
CDI unit, spark plug analysis, troubleshooting
Cooling System:
Radiator, hoses, coolant specifications, leak testing
Transmission:
Clutch operation, gearbox disassembly/assembly, lubrication, troubleshooting
Suspension:
Front fork (KYB) disassembly, oil change, seal replacement, rear shock absorber service, linkage lubrication
Brakes:
Hydraulic system, caliper overhaul, pad replacement, fluid bleeding, disc inspection
Electrical System:
Wiring diagrams, lighting, charging system (stator, rectifier), troubleshooting
Chassis Frame:
Frame inspection, subframe maintenance, footpeg assembly
Bodywork:
Seat, fuel tank, side panels, fender removal and installation
Wheels Tires:
Spoke tensioning, wheel bearing service, tire pressure recommendations
Maintenance:
Scheduled maintenance, oil changes, filter replacements, chain adjustment, spark plug replacement
Troubleshooting:
Diagnostic flowcharts, common problems and solutions, symptom-based repair guides
Repair:
Detailed step-by-step instructions for all major components and systems
Rebuilds:
Engine rebuild, carburetor overhaul, suspension rebuild
Diagnostics:
Electrical testing, component testing, performance analysis
Depth:
Comprehensive - from basic maintenance to complete engine and transmission overhauls, including detailed torque specifications and clearances.
Engine Type:
Liquid-cooled, four-stroke, single-cylinder, DOHC
Bore X Stroke:
89.0 mm x 77.0 mm
Compression Ratio:
12.0:1
Horsepower:
Approx. 50 HP (at crank, estimated)
Torque:
N/A (Specific figures not commonly published for competition models)
Carburetor Type:
Keihin FCR 39 (Flat CR Special)
Fuel Type:
Unleaded gasoline (minimum 91 octane recommended)
Oil Type:
Yamalube 4-stroke motorcycle oil (SAE 10W-40 or 20W-40 recommended, API SG or higher)
Oil Capacity:
1.1 L (1.2 US qt)
Type:
Constant-mesh, 5-speed
Clutch Type:
Wet, multiple-disc
Gear Ratios:
1st: 2.167, 2nd: 1.750, 3rd: 1.400, 4th: 1.136, 5th: 0.917
Transmission Oil:
Yamalube 4-stroke motorcycle oil (same as engine oil)
Transmission Oil Capacity:
0.68 L (0.7 US qt)
Safety Rating:
N/A (Competition off-road vehicle, not subject to road safety regulations)
Braking System:
Hydraulic disc brakes, front and rear
Suspension Performance:
Advanced suspension for optimal control and rider comfort on rough terrain
Frame Construction:
Lightweight yet robust aluminum frame for stability
Ergonomics:
Designed for rider control and maneuverability in demanding conditions
Engine Oil Change:
Every 5-10 hours of riding or annually, whichever comes first.
Air Filter Cleaning:
After every few rides, or more frequently in dusty conditions.
Spark Plug Inspection:
Every 10-15 hours of riding.
Chain Lubrication Adjustment:
Regularly, check tension before each ride.
Brake Fluid Flush:
Annually or as needed.
Engine Oil:
Yamalube 4-stroke motorcycle oil (SAE 10W-40 or 20W-40, API SG or higher)
Brake Fluid:
DOT 4 hydraulic brake fluid
Coolant:
Yamaha's permanent antifreeze (or equivalent) mixed 50/50 with distilled water
Engine Reliability:
Early four-strokes could be sensitive to oil changes and proper jetting. Some cases of valve guide wear reported with high mileage.
Carburetion:
Keihin FCR carbs require precise tuning for optimal performance; can be prone to clogging if fuel quality is poor.
Suspension:
KYB forks and rear shock can require regular seal and oil maintenance to maintain performance. Some owners upgrade to later model suspension components.
Clutch:
Clutch plates can wear over time, especially under heavy use; check for slippage.
Brand History:
Yamaha has a long and successful history in motorcycle racing, particularly in motocross, dating back to the early days of the sport.
Predecessors:
Yamaha YZ400 (2-stroke), YZ426F (later model)
Significance:
The YZ400F marked a significant shift for Yamaha in the open-class motocross segment, introducing a competitive four-stroke platform.
Production Years:
1998-1999
Manufacturing Location:
Japan
