Category:
Motocross / Off-Road Motorcycle
Era:
Late 1980s motocross technology.
Competitors:
Honda CR125R, Kawasaki KX125, Suzuki RM125, KTM 125.
Engine Type:
High-performance 125cc two-stroke, liquid-cooled.
Suspension Type:
Advanced suspension systems for its era (e.g., Kayaba forks).
Design Philosophy:
Lightweight, agile, and powerful for competitive motocross racing.
Engine:
Complete engine overhaul, carburetor tuning, ignition system, cooling system (liquid-cooled), lubrication.
Transmission:
Gearbox maintenance, clutch operation, shift mechanism, gearbox oil.
Chassis Suspension:
Front fork (telescopic, cartridge type), rear monoshock suspension, linkage system, swingarm.
Brakes:
Front disc brake system, rear drum brake system, hydraulic components, pad replacement, bleeding procedure.
Electrical System:
Wiring diagrams, lighting system, ignition coil, CDI unit, battery charging system (if applicable).
Fuel System:
Fuel tank, petcock, fuel lines, carburetor model and specifications.
Exhaust System:
Exhaust pipe, silencer, mounting hardware.
Maintenance:
Routine checks, oil changes, filter replacements, chain adjustment, spark plug service, coolant flush.
Troubleshooting:
Diagnostic guides for common problems, symptom-based troubleshooting trees.
Repair:
Step-by-step instructions for component removal, disassembly, inspection, repair, and reassembly.
Disassembly Reassembly:
Detailed guidance on disassembling and reassembling major vehicle components.
Specifications Settings:
Torque specifications, valve clearances (if applicable), ignition timing, carburetor jetting.
Level:
Comprehensive workshop level, suitable for both amateur mechanics and professional technicians.
Detail Level:
Illustrated with clear, step-by-step instructions and detailed diagrams.
Engine Type:
123cc, Liquid-Cooled, Reed Valve, 2-Stroke, Single-Cylinder
Bore X Stroke:
Approx. 56.0 mm x 49.8 mm (refer to manual for exact specs)
Compression Ratio:
Refer to manual (typically high for 2-stroke performance)
Ignition:
CDI (Capacitor Discharge Ignition)
Carburetor:
Mikuni VM Series (specific model and jetting in manual)
Horsepower:
Estimated 35-40 HP (refer to manual for exact dyno data)
Fuel Type:
Unleaded gasoline (91 octane or higher recommended) mixed with 2-stroke oil
Fuel Ratio:
Refer to manual for specific oil-to-fuel ratio (e.g., 20:1, 25:1, 32:1, 40:1)
Fuel Tank Capacity:
Approx. 8.0 Liters (1.9 Gallons) - refer to manual
Type:
6-Speed Manual Constant Mesh
Gear Ratios:
Detailed in manual, optimized for motocross performance.
Gearbox Oil Type:
SAE 80W API GL-4 Hypoid Gear Oil (refer to manual for specific Yamalube or equivalent)
Capacity:
Refer to manual (typically around 0.7 - 1.0 Liters)
Length:
Refer to manual (approx. 2155 mm / 84.8 in)
Width:
Refer to manual (approx. 805 mm / 31.7 in)
Height:
Refer to manual (approx. 1270 mm / 50.0 in)
Dry Weight:
Refer to manual (approx. 95 kg / 209 lbs)
Wet Weight:
Refer to manual (includes all fluids)
Front Tire Size:
80/100-21 (refer to manual for specific OE recommendations)
Rear Tire Size:
100/90-19 (refer to manual for specific OE recommendations)
Wheelbase:
Refer to manual (approx. 1450 mm / 57.1 in)
Front Travel:
Refer to manual (e.g., 275mm - 300mm)
Rear Travel:
Refer to manual (e.g., 280mm - 300mm)
Not Applicable:
Motorcycles of this era did not typically have standardized crash ratings.
Braking:
Front hydraulic disc brake, rear drum brake for effective stopping power.
Frame Construction:
Steel semi-double cradle frame for rigidity and rider control.
Rider Position:
Designed for aggressive off-road riding posture.
Not Applicable:
This is a performance motocross bike; no infotainment systems.
Not Applicable:
No electronic driver assistance features are present on this model.
Not Applicable:
No connectivity features are present on this model.
Cdi System:
Advanced for its time, the CDI unit controls ignition timing for optimal power delivery.
Front Fork Type:
Cartridge-style telescopic forks, offering adjustable damping and preload for precise tuning.
Rear Suspension Type:
Monocross (single shock absorber with linkage system), providing progressive damping and excellent rear-wheel traction.
Oil Change Engine:
Refer to manual (typically based on operating hours or race events for off-road).
Air Filter Cleaning:
Frequent cleaning and re-oiling recommended, especially in dusty conditions.
Spark Plug Replacement:
Refer to manual (typical interval 20-40 hours of operation).
Chain Adjustment:
Regular checks and adjustment required based on play.
Top End Rebuild:
Recommended every 50-100 hours of aggressive use (piston, rings, cylinder inspection).
Coolant:
High-quality ethylene glycol-based antifreeze mixed with distilled water (typically 50/50 ratio). Refer to manual for specific type and capacity.
Brake Fluid:
DOT 3 or DOT 4 brake fluid (refer to manual for precise specification).
Power Valve System:
Can sometimes be a source of wear or sticking if not maintained; manual will detail inspection and cleaning.
Clutch Wear:
Regular adjustment and inspection of clutch plates and springs are necessary due to high-performance use.
Suspension Seals:
Fork and shock seals can wear over time and require periodic replacement to prevent leaks.
Carburetor Cleaning:
Routine cleaning of the carburetor jets and passages is crucial for optimal performance.
Manufacturer:
Yamaha Motor Company, known for its long history in motorsports and motorcycle manufacturing.
Yz Lineage:
The YZ series has a distinguished racing pedigree, with the YZ125 being a staple in the 125cc motocross class for decades.
1989 Updates:
The 1989 model likely incorporated refinements over previous years, possibly including updated suspension, engine tuning, or chassis geometry.
Production Period:
Continuous production of the YZ125 model spanning several decades.
