Segment:
Motocross / Off-Road Competition
Target User:
Enthusiast riders, mechanics, and race teams performing maintenance and repairs.
Key Competitors:
Honda CR250, Kawasaki KX250, Suzuki RM250, KTM 250 EXC/SX (during this era).
Model Strengths:
Renowned for strong mid-range power, agile handling, and reliability in its class.
Manual Value Proposition:
Provides essential information for owners to maintain peak performance and prolong the life of their vintage YZ250.
Engine Systems:
Top-end overhaul (piston, rings, cylinder, head), bottom-end assembly (crankshaft, connecting rod, bearings), cooling system (if applicable, though YZ250 is typically air-cooled for this period), lubrication systems, fuel system (carburetor, intake), exhaust system, ignition system (CDI, spark plug).
Transmission Drivetrain:
Clutch assembly and operation, gear shifting mechanism, transmission gear ratios, final drive (chain and sprockets).
Chassis Suspension:
Front suspension (fork disassembly, seal replacement, oil levels, adjustments), rear suspension (monoshock, linkage, shock absorber servicing, spring preload), frame inspection and repair.
Brakes:
Front and rear brake systems (hydraulic disc brakes), caliper overhaul, master cylinder servicing, brake fluid type and bleeding procedures, rotor and pad specifications.
Electrical:
Wiring diagrams, lighting system (if applicable), ignition coil, CDI unit, stator, troubleshooting electrical faults.
Fuel System:
Carburetor model (e.g., Keihin PWK), jetting specifications, float bowl adjustment, throttle cable routing and adjustment.
Routine Maintenance:
Pre-ride inspections, chain adjustment and lubrication, air filter cleaning/replacement, spark plug inspection and replacement, coolant checks (if applicable), brake pad inspection, tire pressure checks.
Component Overhaul:
Engine top-end rebuild (piston kit, cylinder honing), crankshaft and connecting rod replacement, clutch pack replacement, transmission gear inspection and replacement, carburetor rebuild and adjustment, suspension fork and shock absorber servicing.
Troubleshooting:
Diagnostic flowcharts for common issues such as starting problems, poor running, clutch slippage, suspension leaks, brake fade.
Diagnostic Procedures:
Compression testing, ignition system testing (spark plug condition, timing checks), carburetor circuit testing.
Depth Level:
Comprehensive from basic user maintenance to full engine and chassis rebuilds.
Engine Type:
2-Stroke, Liquid-Cooled (typically for YZ250 of this era, though some earlier models were air-cooled - manual would specify)
Engine Displacement:
249cc
Bore X Stroke:
68.0 mm x 68.0 mm (typical for this generation)
Compression Ratio:
Typically around 8.5:1 to 9.0:1 (manual will provide exact spec)
Valve Actuation:
Reed Valve Intake
Ignition System:
CDI (Capacitor Discharge Ignition)
Carburetor:
Keihin PWK series (e.g., PWK38 or similar, manual will specify exact model and size)
Horsepower:
Approx. 45-50 HP (at crankshaft, typical for this class and era)
Torque:
Approx. 30-34 lb-ft (at crankshaft, typical)
Fuel Type:
Unleaded Gasoline (91 Octane or higher recommended, pre-mix required)
Fuel Mixture:
2-Stroke Pre-mix (Yamaha recommended 2-stroke oil, typically 32:1 or 50:1 ratio - manual will specify)
Engine Oil Type:
2-Stroke Engine Oil (JASO FD or equivalent recommended)
Transmission Oil Capacity:
Approx. 0.7 - 0.8 Liters (manual will specify exact amount and type, typically SAE 10W-30 or 10W-40 API SE/SF)
Cooling System Capacity:
N/A (typically air-cooled for YZ250 of this period, or if liquid-cooled, capacity specified in manual)
Overall Length:
Approx. 84.5 - 85.5 inches (manual will provide exact)
Overall Width:
Approx. 32.0 - 32.5 inches (manual will provide exact)
Overall Height:
Approx. 50.0 - 51.0 inches (manual will provide exact)
Wheelbase:
Approx. 57.5 - 58.0 inches (manual will provide exact)
Dry Weight:
Approx. 210 - 215 lbs (manual will provide exact, without fluids)
Curb Weight:
Approx. 225 - 230 lbs (manual will provide exact, with all fluids)
Front Suspension Travel:
Approx. 11.8 inches (300mm) (manual will specify exact)
Rear Suspension Travel:
Approx. 11.8 inches (300mm) (manual will specify exact)
Front Wheel Size:
21 inch
Front Tire Size:
80/100-21 (manual will specify recommended brands/models)
Rear Tire Size:
110/90-18 (manual will specify recommended brands/models)
Oil Change Interval:
Transmission oil should be checked and changed per the manual's recommendations, typically every 15-25 hours of operation or annually.
Air Filter Cleaning:
Recommended to clean and re-oil after every few rides or as conditions dictate, especially in dusty environments.
Spark Plug Replacement:
Inspect every 5-10 hours, replace as needed. Manual will specify recommended plug type (e.g., NGK BR7ES).
Top End Rebuild:
Recommended every 50-100 hours of aggressive riding, or when compression drops. Manual details the process and specifications for piston, rings, and cylinder inspection/replacement.
Fork Oil Type Level:
Manual will specify the precise grade of fork oil (e.g., Showa SS-07, KYB 0W-30) and the oil level in mm or volume.
Brake Fluid Type:
DOT 3 or DOT 4 (manual will specify exact type and replacement intervals).
Common Wear Items:
Clutch plates, piston rings, crank bearings, wheel bearings, steering head bearings, fork seals, shock seals.
Engine Specific Considerations:
Proper pre-mix ratio is critical. Overheating can damage the piston and cylinder. Carburetor jetting adjustments are common based on altitude and temperature.
Suspension Maintenance:
Regular fork and shock servicing is essential to maintain optimal damping and prevent seal leaks. The manual provides detailed procedures for this.
Yamaha Motorcycles:
Yamaha Motor Corporation has a long-standing legacy in motorsports, particularly in motocross and off-road racing, dating back to the 1960s.
Yz Series Legacy:
The YZ series has been a cornerstone of Yamaha's off-road lineup, evolving significantly over decades. The YZ250 has consistently been a benchmark for performance and innovation in the 250cc two-stroke class.
Yz250 Production Era:
The YZ250 has been in continuous production in various forms since the 1970s. The 1990-1995 models represent a specific generation known for its competitive performance in AMA Motocross and Supercross.
Model Specific Developments
1990S Yz250 Updates:
During the early to mid-1990s, Yamaha made significant updates to the YZ250, including chassis refinements, suspension improvements (e.g., Kayaba front forks), engine tuning for broader powerbands, and often updated bodywork. The manual will reflect the specific configuration of these years.
