Positioning:
The Yamaha YZ250 in 2004 was a highly competitive and popular motocross machine, known for its potent two-stroke power and agile handling. This manual caters to enthusiasts and professional mechanics maintaining this specific performance-oriented model.
Competitors:
Honda CR250R, Kawasaki KX250, Suzuki RM250
Features:
Represents a critical era for 250cc two-stroke motocross bikes, offering a direct connection to the performance and maintenance requirements of a legendary machine.
Primary Coverage:
Complete service, repair, diagnosis, and maintenance
Secondary Coverage:
Troubleshooting, technical specifications, adjustments
Estimated Pages:
Likely 300-500 pages (typical for a comprehensive workshop manual of this era)
Type:
Workshop Service Repair Manual
Format:
Downloadable Digital File (PDF)
Engine:
Top-end rebuild, bottom-end assembly, cooling system (if applicable), lubrication, performance tuning
Transmission:
Clutch assembly, gear shifting mechanism, gearbox disassembly and assembly, oil specifications
Fuel System:
Carburetor inspection, cleaning, adjustment, jetting, fuel lines, fuel tank maintenance
Ignition System:
Spark plug specifications, CDI unit, stator, wiring diagrams
Suspension:
Front fork (KYB) disassembly, seal replacement, oil type and level, rear shock absorber service, spring rates, adjustments
Brakes:
Front and rear hydraulic brake system, caliper service, master cylinder overhaul, fluid type (DOT 4), bleeding procedures, pad replacement
Electrical System:
Wiring diagrams, lighting (if equipped), kill switch, troubleshooting electrical faults
Frame And Bodywork:
Frame inspection, plastic body panel removal and installation, seat maintenance
Cooling System:
Radiator maintenance, coolant type and capacity (if water-cooled, YZ250 is typically air-cooled, but manual may cover related components)
Exhaust System:
Pipe and silencer inspection, packing replacement (silencer)
Maintenance:
Regular service checks, lubrication points, air filter cleaning/replacement, chain adjustment, oil changes (gearbox)
Troubleshooting:
Diagnostic flowcharts for common starting, running, and performance issues
Repair:
Complete disassembly and reassembly instructions for all major components
Adjustments:
Carburetor settings, clutch lever free play, brake lever adjustments, suspension clicker adjustments
Diagnostics:
Component testing, electrical system diagnosis, compression testing
Depth:
Comprehensive, covering routine maintenance to full engine and transmission rebuilds
Diagnostic Capabilities:
Advanced diagnostic procedures and troubleshooting guides
Rebuild Procedures:
Detailed instructions for engine, transmission, and suspension component rebuilds
Type:
2-Stroke, Liquid-Cooled (Note: While the 2004 YZ250 is typically air-cooled, the manual may reference liquid-cooling in general Yamaha context or for specific components not on this model. Confirming air vs. liquid cooling is crucial.)
Bore X Stroke:
66.4 mm x 72.0 mm
Compression Ratio:
8.2:1 (as quoted in some specifications, can vary slightly based on source)
Intake System:
Reed Valve
Horsepower:
Approx. 40-45 HP (Estimates, actual dyno figures vary)
Torque:
Approx. 25-30 lb-ft (Estimates)
Carburetor:
Keihin PWK38S (38mm) (Standard specification for this model)
Fuel Type:
Unleaded Gasoline (90+ Octane Recommended)
Premix Ratio:
50:1 (Yamalube 2R or equivalent 2-stroke oil)
Oil Change Gearbox:
Every 10-15 hours of riding, or as specified in manual.
Air Filter Cleaning:
Every 5-10 hours of riding, or after each wet ride.
Spark Plug Inspection:
Every 10-15 hours of riding.
Chain Lubrication And Adjustment:
Every 5-10 hours of riding.
Engine Top End Rebuild:
Varies greatly based on usage and riding style; typically 30-50 hours for competitive use.
Transmission Oil:
Yamalube SAE 10W-30 API SG or higher (refer to manual for exact specification and capacity)
Coolant:
If liquid-cooled, use Yamaha's Super Coolant or a quality ethylene glycol-based coolant mixed 50/50 with distilled water. (Note: YZ250 is typically air-cooled, this is for general reference if the manual covers any liquid-cooled aspects).
Brake Fluid:
DOT 4 (refer to manual for confirmation)
Fork Oil:
Yamalube Fork Oil G10 or equivalent SAE 0W-20 (Refer to manual for specific type and volume per fork leg)
Common Issues:
Wear on clutch plates, potential carbon buildup in exhaust port, carb jetting sensitivity to altitude/temperature, fork seal leaks with aggressive use.
Preventative Maintenance:
Regular cleaning of air filter and carburetor, proper premix ratio, timely gearbox oil changes, keeping chain adjusted and lubricated.
Heritage:
Yamaha has a long and storied history in motocross, with the YZ line being a cornerstone of their performance off-road offerings for decades.
Evolution:
The 2004 YZ250 represented an evolution of Yamaha's successful 250cc two-stroke platform, incorporating refinements in suspension, chassis, and engine performance. It continued the legacy of its predecessors, offering a potent motocross weapon.
Production Era:
The YZ250 two-stroke was produced for many years, with the 2004 model being part of a highly competitive generation before the shift towards four-stroke technology became more dominant.
