Historical Context:
The 1998 Yamaha YZ250 was a prominent contender in the 250cc two-stroke motocross class, known for its powerful engine and competitive chassis. This manual targets owners and technicians maintaining these sought-after machines.
Key Advantages:
Provides factory-level detail essential for the longevity and peak performance of the YZ250, crucial for competitive use or passionate ownership.
Manual Value:
Offers 'no extra fees, no expiry dates,' ensuring a perpetual resource for vehicle upkeep.
Engine System:
Complete overhaul, troubleshooting, tuning, lubrication, cooling (liquid cooling system)
Transmission System:
Clutch operation, gearbox disassembly, assembly, gear ratios, shift mechanism
Chassis System:
Frame inspection, suspension (forks and rear shock absorber), steering, bearings
Braking System:
Hydraulic brake system, caliper service, master cylinder, fluid replacement, pad wear
Electrical System:
Ignition system, lighting, wiring diagrams, battery maintenance, stator, CDI unit
Fuel System:
Carburetor tuning and overhaul, fuel lines, fuel tank maintenance
Exhaust System:
Pipe inspection, packing replacement (silencer)
Plastics And Bodywork:
Repair and replacement of fenders, shrouds, seat, and other body panels.
Maintenance Tasks:
Regular servicing, oil changes, filter replacements, chain adjustment, spark plug service
Repair Tasks:
Engine rebuild, transmission repair, suspension overhaul, brake caliper rebuild, carburetor tuning
Troubleshooting:
Diagnostic charts, common problems and solutions, electrical fault finding
Technical Specifications:
Torque specifications, clearances, fluid types, capacities, electrical resistance values
Frame And Suspension Alignment:
Procedures for checking and adjusting frame alignment and suspension geometry.
Wheel And Tire Service:
Tire mounting/dismounting, tube replacement, spoke tightening, wheel balancing.
Depth:
Comprehensive: From basic rider maintenance to full engine and transmission rebuilds
Wiring Diagram Complexity:
Detailed, component-level wiring diagrams for accurate electrical diagnosis and repair.
Engine Type:
2-Stroke, Single Cylinder, Reed Valve
Bore X Stroke:
68.0 mm x 68.0 mm
Compression Ratio:
8.2:1 (Nominal)
Horsepower Estimated:
~45-50 hp (at crankshaft)
Torque Estimated:
~30-35 lb-ft (at crankshaft)
Carburetor Model:
Keihin PWK38 (typically)
Fuel Type:
Unleaded gasoline with proper 2-stroke oil pre-mix
Premix Ratio:
50:1 (Recommended, specific oil type in manual)
Crankcase Type:
2-stroke oil injection (Autolube) or pre-mix
Cooling Method:
Liquid-Cooled
Ignition Type:
Digital CDI (Capacitor Discharge Ignition)
Transmission Type:
Constant-mesh, 5-speed
Clutch Type:
Wet, multi-plate
Gear Ratios:
Refer to manual for specific ratios (e.g., 1st: 2.917, 2nd: 2.167, 3rd: 1.667, 4th: 1.350, 5th: 1.130)
Transmission Oil Type:
Yamalube Gear Oil or equivalent (refer to manual for specific viscosity and API rating)
Transmission Oil Capacity:
~0.7 Liters (Check dipstick/level plug)
Infotainment System:
N/A (Off-road racing motorcycle, no infotainment features)
Assistance Features:
N/A (Designed for rider skill, no electronic rider aids)
Connectivity Features:
N/A (No electronic connectivity features)
Power Delivery:
Two-stroke engine with strong mid-range and top-end power, optimized for motocross track performance.
Oil Change Frequency:
Every 10-15 hours of riding, or as per manual recommendations for drivetrain oil.
Air Filter Cleaning:
After every few rides, or more frequently in dusty conditions.
Spark Plug Replacement:
Check and clean regularly, replace as needed based on condition (refer to manual for specific type and gap).
Top End Rebuild:
Recommended every 40-80 hours of aggressive riding (piston, rings, cylinder inspection).
Engine Oil Type:
High-quality 2-stroke premix oil (e.g., Yamalube 2-stroke oil) at 50:1 ratio. Refer to manual for specific approval standards.
Coolant Type:
Permanent type antifreeze coolant mixed with distilled water (50/50 ratio). Refer to manual for specific type and capacity.
Brake Fluid Type:
DOT 3 or DOT 4 hydraulic brake fluid (refer to manual for specific type and replacement interval).
Common Wear Items:
Clutch plates, piston rings, exhaust packing, wheel bearings, steering head bearings, suspension seals.
Carburetor Tuning:
Carburetor jetting may require adjustment based on altitude, temperature, and modifications.
Power Valve Maintenance:
The exhaust power valve system requires periodic cleaning to prevent carbon buildup and ensure proper operation.
Yamaha Legacy:
Yamaha has a long and successful history in dirt bike racing, with the YZ line being a cornerstone of their motocross offerings for decades.
Yz250 Development:
The 1998 model represents a refinement of the YZ250 platform, incorporating technological advancements and design improvements over preceding years to remain competitive.
Manufacturing Origin:
Japan (Primary manufacturing location for Yamaha)
