Segment:
Competition Motocross (MX)
Target User:
Motocross riders, mechanics, and enthusiasts seeking detailed maintenance and repair guidance for the 1998 YZ125.
Competitors:
Honda CR125R, Kawasaki KX125, Suzuki RM125.
Model Focus:
The 1998 YZ125 was a significant model in Yamaha's competitive motocross lineup, known for its performance and handling.
General Coverage:
Comprehensive service, repair, and workshop information for the 1998 Yamaha YZ125.
Specific Systems:
Engine, transmission, chassis, suspension, brakes, electrical system, fuel system, cooling system, lubrication system, exhaust system, and bodywork.
Estimated Pages:
300-400 (typical for this era of comprehensive service manuals)
Type:
Service Repair Workshop Manual
Format:
Digital (likely PDF)
Engine:
Complete engine disassembly, assembly, component inspection, troubleshooting, and specifications for the 125cc two-stroke engine.
Transmission:
Gearbox inspection, repair, clutch service, and shift mechanism adjustments.
Suspension:
Front fork (KYB or similar) and rear monoshock (Pro-Link or similar) disassembly, service, oil changes, seal replacement, and tuning.
Brakes:
Front and rear hydraulic disc brake system service, including caliper overhaul, pad replacement, bleeding procedures, and master cylinder repair.
Electrical System:
Ignition system, lighting, wiring diagrams, battery maintenance, and troubleshooting of electrical components.
Fuel System:
Carburetor (likely Keihin PWK or similar) disassembly, cleaning, jetting, fuel tank maintenance, and fuel line checks.
Maintenance:
Routine checks, fluid changes (engine oil, coolant), filter cleaning/replacement, chain lubrication, and general upkeep.
Repair:
Detailed step-by-step instructions for component repair and replacement, including engine rebuild, suspension service, and brake caliper overhaul.
Troubleshooting:
Diagnostic charts and symptom-based troubleshooting guides for common mechanical and electrical issues.
Disassembly Assembly:
Complete instructions for dismantling and reassembling all major motorcycle components.
Depth:
Comprehensive, suitable for both experienced mechanics and determined DIY enthusiasts. Covers everything from basic adjustments to full engine rebuilds.
Engine Type:
125cc, Liquid-Cooled, Two-Stroke, Reed Valve Induction
Bore X Stroke:
54.0 mm x 54.5 mm (typical for this generation)
Compression Ratio:
8.7:1 (typical, may vary slightly)
Carburetor:
Keihin PWK38 (typical)
Horsepower:
Approx. 37-40 HP (stock, estimated)
Torque:
Approx. 18-20 lb-ft (stock, estimated)
Fuel Type:
Unleaded gasoline (91 octane or higher recommended)
Fuel Mixture:
2-stroke pre-mix (e.g., 32:1 or 40:1 ratio with high-quality 2-stroke oil)
Transmission Oil Type:
Yamaha Gear Oil (or equivalent SAE 80 hypoid gear oil)
Coolant Type:
Yamaha All Weather Yamaha Coolant (or equivalent 50/50 mix of ethylene glycol and distilled water)
Ignition Type:
CDI (Capacitor Discharge Ignition)
Length:
Approx. 2165 mm (85.2 in)
Width:
Approx. 820 mm (32.3 in)
Height:
Approx. 1280 mm (50.4 in)
Wheelbase:
Approx. 1475 mm (58.1 in)
Ground Clearance:
Approx. 350 mm (13.8 in)
Dry Weight:
Approx. 95 kg (209 lbs)
Wet Weight:
Approx. 102 kg (225 lbs) (estimated)
Fuel Tank Capacity:
8.2 L (2.2 US gal)
Oil Tank Capacity:
0.7 L (0.74 US qt) (Autolube system)
Safety Classification:
N/A (Competition Off-Road Vehicle)
Brakes:
Hydraulic disc brakes front and rear for superior stopping power.
Suspension:
Long-travel suspension for absorbing impacts and maintaining control over rough terrain.
Ergonomics:
Designed for rider control and comfort during demanding motocross conditions.
Engine Oil Change:
Refer to manual for specific intervals based on operating hours or mileage; typically every 10-20 hours for rigorous use.
Air Filter Cleaning:
Clean after every few rides or as dictated by dusty conditions.
Spark Plug Check:
Inspect and clean/replace as needed, typically every 20-40 hours.
Chain Lubrication Adjustment:
Lubricate before every ride, adjust tension as needed.
Suspension Service:
Fork oil change and seal inspection typically every 20-40 hours, full suspension service as needed.
Transmission Oil Capacity:
Approx. 0.8 L (0.85 US qt)
Fork Oil Type:
Yamalube Fork Oil G10 or equivalent (e.g., 5W or 10W)
Fork Oil Level:
Refer to manual for precise level measurement (e.g., 100-120mm)
Carburetor Tuning:
Can be sensitive to altitude and temperature changes; requires precise jetting.
Clutch Wear:
Clutch plates can wear with aggressive riding; require regular inspection and adjustment.
Power Valve Operation:
The power valve system can accumulate carbon and require cleaning for optimal performance.
Suspension Seals:
Fork and shock seals can degrade over time and require replacement to prevent leaks.
Yamaha Motorcycles:
Yamaha has a long and storied history in motorcycle racing, particularly in motocross, with a reputation for innovation and performance.
Yz125 Lineage:
The YZ125 has been a cornerstone of Yamaha's motocross efforts since its inception, undergoing continuous development and refinement.
1998 Updates:
The 1998 model likely saw refinements to suspension, engine tuning, and chassis components to remain competitive.
Production Period:
The YZ125 has been in continuous production for decades, making it a popular and enduring model.
