Segment:
Performance Motocross (250cc Class)
Competitors 2005:
Honda CR250R, Kawasaki KX250, Suzuki RM250, KTM 250 SX
Engine Character:
Potent, Rev-Happy Two-Stroke Powerband
Handling:
Renowned for Agile and Predictable Handling
Value Proposition:
Essential resource for owners and mechanics to maintain optimal performance and longevity.
Target Audience:
Yamaha YZ250 Owners, DIY Mechanics, Professional Technicians
Engine System:
Complete Engine Teardown, Rebuild, Diagnosis, and Tuning
Transmission System:
Gearbox Removal, Inspection, Reassembly, and Fluid Specifications
Clutch System:
Clutch Assembly, Operation, Maintenance, and Troubleshooting
Cooling System:
Radiator, Hoses, Water Pump, and Coolant Specifications
Fuel System:
Carburetor Adjustment, Cleaning, Jetting, and Fuel Delivery System
Ignition System:
CDI, Spark Plug, Coil, and Timing Specifications
Exhaust System:
Pipe and Silencer Maintenance and Specifications
Suspension System Front:
Fork Disassembly, Reassembly, Oil Levels, and Valving Specifications
Suspension System Rear:
Monoshock, Linkage, Shock Absorber Service, and Adjustment
Brakes System Front:
Caliper, Master Cylinder, Pad Replacement, and Fluid Bleeding
Brakes System Rear:
Caliper, Master Cylinder, Pad Replacement, and Fluid Bleeding
Wheels And Tires:
Wheel Bearing Service, Tire Selection, and Pressure Recommendations
Electrical System:
Lighting, CDI Unit, Basic Wiring Diagrams (limited for MX)
Frame And Bodywork:
Chassis Components, Body Panel Removal and Installation
Maintenance Tasks:
Routine Service, Oil Changes, Filter Cleaning, Chain Adjustment, Lubrication
Troubleshooting:
Diagnostic Procedures for Common Issues, Symptoms, and Causes
Repair Procedures:
Step-by-step instructions for component replacement and repair
Rebuild Procedures:
Complete Engine Teardown and Reassembly
Adjustment Procedures:
Carburetor, Suspension, Clutch, and Throttle Cable Adjustments
Inspection Procedures:
Pre-ride Checks, Component Wear Inspection
Depth:
Comprehensive Engine Rebuild and Advanced Component Service
Diagnostics:
Detailed Troubleshooting Guides and Flowcharts
Visual Aids:
Includes Pictures and Diagrams
Bore X Stroke:
66.4 mm x 72.0 mm
Compression Ratio:
9.3:1 (Nominal)
Engine Configuration:
Single Cylinder, Liquid-Cooled, Reed Valve, Two-Stroke
Intake System:
Yamaha Power Valve System (YPVS)
Lubrication:
Pre-mix (Fuel/Oil Mixture)
Horsepower Estimated:
Approx. 45-48 HP (at Crankshaft, varies with tuning)
Torque Estimated:
Approx. 29-31 lb-ft (at Crankshaft, varies with tuning)
Carburetor Model:
Keihin PWK38S (38mm Slide Carburetor)
Fuel Type Recommended:
91 Octane Unleaded Gasoline
Oil Type Recommended:
2-Stroke Premix Oil (JASO FD/FC or API TC rated)
Fuel Oil Ratio Recommended:
50:1 (Consult Manual for specific recommendations)
Oil Change Interval Engine:
Consult manual; typically requires top-end rebuilds at regular intervals based on usage hours/race conditions.
Air Filter Cleaning:
Frequent cleaning recommended, especially after dusty rides (e.g., after every few rides).
Spark Plug Replacement:
Check and clean/replace as needed based on performance. Typical interval 10-20 hours of use.
Chain Adjustment:
Check and adjust regularly, especially during break-in and after heavy use.
Fork Oil Type:
Yamalube Fork Oil G10 or equivalent (specific viscosity and level detailed in manual).
Transmission Oil Type:
Yamalube 10W-30 API SE or SF (specific recommendations in manual).
Brake Fluid Type:
DOT 3 or DOT 4 Hydraulic Brake Fluid
Typical Wear Items:
Piston, piston rings, clutch plates, brake pads, bearings.
Carburetor Jetting Variability:
Requires careful jetting based on altitude, temperature, and riding conditions.
Clutch Lever Feel:
May require periodic adjustment for optimal engagement.
Yamaha Motocross Legacy:
Yamaha has a long and storied history in motocross, with the YZ line being a cornerstone of their off-road racing success.
Yz250 Evolution Notes:
The YZ250 has been a consistent performer, receiving updates for suspension, chassis, and engine components throughout its lineage. The 2005 model represents a mature iteration of the platform.
Production Era:
YZ250 models have been in continuous production for decades.
