Positioning:
Essential diagnostic and repair resource for owners and mechanics of 1997-1998 Yamaha YZ125 motocross bikes.
Competitors:
Generic service guides, manufacturer-specific but limited online forums.
Features:
Instant download, comprehensive coverage, detailed diagrams, easy-to-follow instructions.
Engine:
Complete overhaul, tuning, carburetor, ignition, lubrication, cooling (liquid-cooled), exhaust
Transmission:
Gearbox disassembly, assembly, inspection, clutch operation, chain drive
Chassis:
Frame inspection and repair, suspension (forks, shock absorber), steering system, swingarm
Brakes:
Hydraulic front and rear brake systems, caliper, master cylinder, brake lines, bleeding procedures
Electrical:
Wiring diagrams, lighting system, ignition system components, troubleshooting electrical faults
Fuel System:
Fuel tank, fuel lines, carburetor tuning and rebuilding, jetting specifications
Maintenance:
Regular servicing, lubrication points, filter replacement, spark plug checks, chain adjustment
Troubleshooting:
Diagnostic flowcharts, common problem identification and solutions for engine, chassis, and electrical systems
Repair:
Detailed step-by-step instructions for component removal, disassembly, repair, reassembly, and installation
Overhaul:
Complete engine rebuild procedures, including piston replacement, ring installation, cylinder honing
Technical Specifications:
Torque values, clearances, fluid capacities, ignition timing, compression test procedures
Depth:
Comprehensive, covering all aspects from basic maintenance to complete engine and chassis overhauls
Engine Type:
Liquid-cooled, 2-stroke, reed valve induction
Bore X Stroke:
54.0 mm x 54.5 mm
Compression Ratio:
8.7:1 (approx.)
Horsepower:
Approximately 37-40 HP (varies by tuning and conditions)
Torque:
Not explicitly stated, but designed for strong mid-range power delivery.
Carburetor Model:
Mikuni TMX38 (typically)
Fuel Type:
Unleaded gasoline with 2-stroke oil premix (e.g., 50:1 ratio)
Carburetor Jetting Specs:
Detailed jetting specifications for various altitudes and conditions are provided in the manual.
Ignition System:
CDI (Capacitor Discharge Ignition)
Lubrication Type:
Premix lubrication
Cooling System:
Liquid-cooled
Coolant Type:
Ethylene glycol-based coolant (50% mixture with distilled water)
Transmission Type:
Constant mesh 6-speed sequential
Gear Ratios:
Detailed gear ratios for each speed are provided in the manual.
Clutch Type:
Wet, multi-plate
Clutch Fluid:
Brake fluid DOT 3 or DOT 4
Clutch Adjustment:
Cable adjustment procedures covered.
Transmission Oil Type:
Yamaha Gear Oil 10W-30 or equivalent motorcycle-specific transmission oil.
Transmission Oil Capacity:
Approximately 0.7 Liters
Length:
Approx. 2110 mm (83.1 in)
Width:
Approx. 805 mm (31.7 in)
Height:
Approx. 1270 mm (50.0 in)
Wheelbase:
Approx. 1445 mm (56.9 in)
Ground Clearance:
Approx. 330 mm (13.0 in)
Seat Height:
Approx. 960 mm (37.8 in)
Dry Weight:
Approx. 90 kg (198.4 lbs)
Wet Weight:
Not specified, but includes fluids and fuel.
Fuel Tank Capacity:
8.0 Liters (2.1 US gal)
Safety Ratings:
N/A (Off-road competition vehicle, not subject to road safety standards)
Braking System:
Hydraulic disc brakes front and rear for superior stopping power.
Suspension System:
Long-travel, adjustable suspension for optimal control on varied terrain.
Frame Construction:
Durable steel or aluminum alloy frame designed for strength and impact resistance.
Oil Change:
Every 5-10 hours of riding, or as specified in the manual based on usage.
Air Filter Cleaning:
After every few rides, or more frequently in dusty conditions.
Spark Plug Check:
Regularly, replace as needed based on condition.
Chain Lubrication Adjustment:
Before every ride, or as needed.
Top End Rebuild:
Recommended every 40-60 hours of hard riding (piston, rings, cylinder inspection).
Two Stroke Oil:
High-quality 2-stroke racing oil, recommended ratio 50:1.
Coolant:
50% Ethylene Glycol Antifreeze / Distilled Water mixture.
Brake Fluid:
DOT 3 or DOT 4.
Transmission Oil:
Yamaha Gear Oil 10W-30 or equivalent.
Common Issues:
Clutch wear, carburetor jetting sensitivity to altitude/temperature, piston/ring wear from hard use, suspension seal leaks.
Preventative Maintenance:
Adhering to strict service intervals, proper jetting, and using high-quality lubricants are crucial for longevity.
Heritage:
Yamaha has a long and successful history in motocross, with the YZ series being a cornerstone of their performance offerings for decades.
Yz Series Evolution:
The YZ125 has undergone continuous development, focusing on engine power, suspension performance, and chassis handling to remain competitive in its class.
Production Years:
The YZ125 has been in production since the 1970s.
Manufacturing Location:
Japan (typically for Yamaha motorcycles)
Motocross Awards:
The YZ125 platform has a history of numerous championships and accolades in amateur and professional motocross racing.
Performance Ratings:
Consistently rated highly for its nimble handling, powerful 2-stroke engine, and competitive price point within its class.
Certifications:
N/A (Competition vehicle).
