Segment:
High-performance Motocross Competition
Target Audience:
Motocross Racers, Mechanics, Enthusiasts
Competitors 2003:
KTM 250 EXC, Honda CR250R, Suzuki RM250, Kawasaki KX250
Engine Design:
Liquid-cooled, 249cc, Reed-valve inducted, YPVS (Yamaha Power Valve System)
Suspension Front:
48mm Inverted Telescopic Fork (SSS - Speed Sensitive System potentially)
Suspension Rear:
Monocross Suspension with Single Shock Absorber
Clarity:
Illustrated with clear, step-by-step instructions
Utility:
Essential for maintaining peak performance and longevity
Primary Coverage:
Complete Service, Repair, and Workshop Procedures
Secondary Coverage:
Maintenance Schedules, Troubleshooting, Diagnostics
Estimated Page Count:
300+
Type:
Service Repair Workshop Manual
Engine:
Complete Overhaul, Top-End, Bottom-End, Carburetion, Ignition System, Cooling System
Transmission:
Clutch, Gearbox, Shifting Mechanism, Lubrication
Chassis:
Frame, Suspension (Front/Rear), Steering, Swingarm, Bearings
Brakes:
Front and Rear Hydraulic Disc Brake System Service, Fluid Replacement, Bleeding
Electrical:
Ignition System (CDI), Lighting, Wiring Diagrams, Battery
Fuel System:
Fuel Tank, Petcock, Carburetor (Mikuni VM38) Disassembly and Reassembly
Maintenance:
Regular Service Checks, Oil Changes, Filter Replacements, Chain Adjustments
Repair:
Engine Rebuilds, Suspension Overhauls, Brake System Repairs, Electrical Component Replacement
Troubleshooting:
Diagnostic Charts for Common Problems, Electrical Troubleshooting
Disassembly Assembly:
Step-by-step guides for major component removal and installation
Depth:
Comprehensive, covering from basic maintenance to full engine and transmission rebuilds
Diagnostic Capabilities:
Detailed fault finding and troubleshooting procedures
Wiring Diagrams:
Included and clearly illustrated
Engine Family:
YZ Series 2-Stroke
Bore X Stroke:
66.4 mm x 72.0 mm
Compression Ratio:
8.2:1 (approximate, may vary with YPVS setting)
Cooling System:
Liquid-cooled
Induction System:
Reed valve
Power Valve System:
YPVS (Yamaha Power Valve System)
Horsepower Estimated:
~45-50 HP (at crankshaft)
Torque Estimated:
~30-33 lb-ft (at crankshaft)
Carburetor Model:
Mikuni VM38
Fuel Type:
Unleaded Gasoline (91 Octane or higher)
Fuel Oil Mix Ratio:
50:1 (Recommended for premix, check manual for specifics)
Type:
5-speed constant mesh
Clutch:
Wet, multi-disc, cable-actuated
Transmission Options:
N/A (Single configuration)
Gear Ratios:
Specific ratios detailed in manual
Transmission Oil Type:
Yamalube 2R or equivalent 2-stroke premix oil (for engine lubrication), Gear Oil SAE 80 API GL-4 (for gearbox, check manual for specific capacity)
Infotainment System:
N/A (Pure competition motocross bike)
Driver Assistance Features:
N/A (Pure competition motocross bike)
Connectivity Features:
N/A (Pure competition motocross bike)
Valve Control:
YPVS (Yamaha Power Valve System) for optimized power delivery across RPM range.
Oil Change Frequency:
As per manual recommendations, typically after every 10-20 hours of racing or a set number of rides.
Air Filter Cleaning:
Frequent cleaning and oiling required, especially in dusty conditions (check manual for frequency).
Spark Plug Replacement:
As needed, based on inspection and performance. Refer to manual for specifications.
Top End Rebuild:
Recommended every 40-60 hours of use, depending on riding style and conditions.
Engine Oil:
Yamalube 2R 100% Synthetic 2-Stroke Oil or equivalent (for pre-mix)
Gearbox Oil:
Yamaha Motorcycle Gear Oil SAE 80 API GL-4 or equivalent (Capacity: 0.75 L / 0.79 US qt)
Coolant:
Yamaha Bio-Degradable Element Coolant or equivalent mixture (50/50 ethylene glycol and distilled water)
Brake Fluid:
DOT 3 or DOT 4 hydraulic brake fluid
Common Wear Items:
Clutch plates, piston, piston rings, reed valves, wheel bearings, steering head bearings, swingarm bearings.
Carburetor Tuning:
Sensitivity to altitude and temperature changes, requiring proper jetting adjustments.
Ypvs System:
Can accumulate carbon and require cleaning or service to ensure proper operation.
Suspension Seals:
Fork seals and shock seals are prone to wear and leaks with hard use.
Brand Focus:
Yamaha has a long-standing reputation for performance-oriented motorcycles, particularly in motocross and off-road racing.
Yz250 Legacy:
The YZ250 has been a dominant force in 250cc motocross for decades, evolving through numerous chassis and engine updates. The 2003 model represents a mature iteration of the aluminum-frame era YZ250.
Production Period Aluminum Frame:
Approximately 1999-2004
Manufacturing Location:
Japan (typically)
Motocross Achievements:
The YZ250 platform has numerous championship wins in various professional motocross and supercross series. Specific awards for the 2003 model year are tied to rider victories.
Motocross Magazine Reviews:
Consistently received high marks for performance, handling, and engine power from leading motocross publications of its era.
Manufacturing Standards:
Built to Yamaha's stringent quality control and performance standards for off-road racing.
