Market Segment:
High-performance motocross competition motorcycle. Known for its potent two-stroke power delivery and agile handling.
Competitors:
Primarily competes with other 250cc two-stroke motocross bikes from brands like Honda (CR250R), Kawasaki (KX250), and Suzuki (RM250) from the same era.
Key Features:
Powerful 249cc liquid-cooled two-stroke engine, advanced suspension (often KYB components), aluminum frame (introduced around this generation), strong braking performance, and Yamaha's reputation for reliability.
Engine Systems:
Top-end (cylinder, piston, rings, head), bottom-end (crankshaft, connecting rod, bearings), lubrication, cooling (air-cooled), fuel system (carburetor, fuel pump), ignition system, exhaust system.
Drivetrain Systems:
Clutch (operation, adjustment, replacement), transmission (gearbox, shift drum, forks), final drive (chain, sprockets).
Chassis Systems:
Frame, suspension (front forks - KYB SSS or similar era, rear shock - KYB or similar era), steering, wheels, brakes (front disc, rear disc), electrical system (lighting, basic wiring).
Maintenance Procedures:
Pre-ride inspection, regular servicing, oil changes, filter cleaning/replacement, chain maintenance, brake fluid flush, spark plug replacement, carburetor cleaning and adjustment.
Repair Procedures:
Complete engine overhaul, piston and ring replacement, crankshaft bearing replacement, clutch rebuild, transmission disassembly and reassembly, suspension fork service (oil change, seal replacement), rear shock absorber service, brake caliper and master cylinder rebuild, wheel bearing replacement.
Troubleshooting Guides:
Diagnostic charts for common running issues, starting problems, performance complaints, and electrical faults.
Depth:
Comprehensive rebuild procedures, detailed exploded views, torque specifications for all fasteners, diagnostic flowcharts, and specific service data for each component.
Engine Code:
Likely 5MW or similar designation for the YZ250 engine of this era.
Engine Description:
249cc, liquid-cooled, reed valve inducted, two-stroke, single-cylinder.
Bore X Stroke:
Approx. 66.4 mm x 72.0 mm
Compression Ratio:
Typically around 8.6:1 to 9.0:1 (check manual for exact specification).
Horsepower:
Estimated 40-45 HP at the crankshaft (actual dyno results vary).
Torque:
Estimated 25-28 lb-ft at the crankshaft (actual dyno results vary).
Carburetor:
Mikuni TMX38mm flat-slide carburetor.
Fuel Type:
Unleaded gasoline, minimum 91 octane recommended. Requires premix of gasoline and 2-stroke oil.
Premix Ratio:
Typically 50:1 or 40:1 with a quality JASO FD certified two-stroke oil. Manual will specify exact ratio and oil type.
Oil Type:
Dedicated 2-stroke engine oil for premix or oil injection system (if equipped, though 2002 YZ250 likely used premix).
Cooling System:
Liquid-cooled, with radiator and fan (if applicable).
Coolant Type:
Mixture of distilled water and ethylene glycol-based antifreeze. Manual will specify ratio and type.
Overall Length:
Approx. 85.2 inches (2165 mm) - typical for this model.
Overall Width:
Approx. 32.5 inches (825 mm) - typical for this model.
Overall Height:
Approx. 50.2 inches (1275 mm) - typical for this model.
Dry Weight:
Approx. 211 lbs (96 kg) - typical for this model.
Fuel Capacity:
Approx. 2.4 gallons (9 liters) - typical for this model.
Wheelbase:
Approx. 58.1 inches (1475 mm) - typical for this model.
Safety Standards:
Designed for competitive off-road use; not road-legal. Safety features focus on operational integrity and rider control.
Braking System:
Hydraulic disc brakes front and rear for strong stopping power.
Suspension Performance:
High-quality adjustable suspension (likely KYB) designed for absorbing impacts and maintaining control over rough terrain.
Frame Construction:
Lightweight and strong aluminum frame provides rigidity and impact resistance.
Oil Change Interval:
Refer to manual for specific intervals, but typically every 5-10 hours of riding for the transmission oil. Engine oil is part of the fuel/air mixture (premix).
Air Filter Cleaning:
Frequent cleaning required, often after every few hours of dusty riding. Manual will detail procedure and cleaning agents.
Spark Plug Replacement:
Intervals vary based on usage, but typically checked or replaced every 10-20 hours of riding. Manual will specify recommended plug type and gap.
Top End Rebuild:
Depending on riding intensity, piston and rings may need replacement every 20-40 hours. Crankshaft and bearings may require service every 50-100 hours. Manual provides wear limits and inspection procedures.
Transmission Oil Type:
Yamaha recommends Yamalube SAE 10W-30 or equivalent API GL-4 gear oil for the transmission. Manual will list exact specifications and capacity.
Brake Fluid Type:
DOT 4 hydraulic brake fluid is standard for most hydraulic brake systems. Manual will confirm type and capacity for front and rear brakes.
Fork Oil Type:
Specific suspension fork oil weight (e.g., 5W or 10W) and quantity. Manual will detail precise type and level.
Common Wear Items:
Clutch plates, piston rings, spark plugs, wheel bearings, chain and sprockets, air filter, fork seals.
Carburetor Tuning:
Two-stroke carburetors require meticulous tuning based on altitude, temperature, and riding conditions. Manual provides baseline settings and adjustment procedures.
Suspension Maintenance:
Regular fork oil changes and seal inspection are critical for maintaining optimal suspension performance and preventing leaks.
Brand Legacy:
Yamaha has a long and successful history in motocross, particularly with its YZ line, known for performance and rider innovation.
Yz250 Evolution:
The YZ250 has been a dominant force in motocross for decades. The 2002 model represented a refinement of the successful platform, likely featuring updates to the chassis, suspension, and engine tuning. This generation saw the adoption of aluminum frames for Yamaha's performance dirt bikes.
Production Period:
2002 model year.
