Category:
Motocross Competition Bike
Target Audience:
Amateur and professional motocross racers, off-road enthusiasts.
Key Competitors Era:
Honda CR125R, Kawasaki KX125, Suzuki RM125, KTM 125 EXC.
Performance Focus:
Lightweight design, strong mid-range power delivery, agile handling.
Technological Advancements Era:
Introduction of the Monocross rear suspension system, advanced reed valve induction, and often a close-ratio gearbox.
Engine Systems:
Top end (cylinder, piston, rings), bottom end (crankshaft, connecting rod, bearings), lubrication, cooling (air-cooled), fuel system (carburetor, fuel tank, petcock), ignition system (CDI, spark plug), exhaust system.
Transmission Systems:
Clutch (operation, adjustment, friction plates), gearbox (gear selection, shift drum, shift forks, bearings), final drive (chain and sprockets).
Chassis Systems:
Frame, suspension (front forks - telescopic, rear monoshock - linkage system), steering system (headstock bearings, handlebars), braking system (front and rear drum brakes for this model year, brake lever, pedal, cables), wheels and tires.
Electrical Systems:
Wiring diagrams, lighting (if applicable for street legality), ignition timing, basic electrical component testing.
Routine Maintenance:
Oil change, air filter cleaning/replacement, spark plug inspection/replacement, chain adjustment, brake adjustment, carburetor cleaning and tuning.
Repair Procedures:
Engine rebuild (top and bottom end), carburetor overhaul, transmission disassembly and reassembly, suspension servicing (fork seal replacement, shock rebuild), brake system maintenance.
Troubleshooting:
Diagnostic charts for common performance issues, starting problems, electrical faults.
Diagnostic Capabilities:
Detailed symptom-based troubleshooting guides, component testing procedures with specifications.
Rebuild Scope:
Comprehensive, covering complete engine disassembly and reassembly, transmission overhaul, suspension component rebuilding.
Special Tools:
Identification and usage of specific Yamaha specialty tools required for certain procedures.
Searchability:
Searchable text content for quick information retrieval.
Image Resolution:
High-resolution diagrams and illustrations for clarity.
Readability:
Clear, legible font and layout.
Binding Type Description:
N/A (Digital format)
Paper Type Description:
N/A (Digital format)
Engine Displacement:
123.6 cc
Bore X Stroke:
57.0 mm x 48.8 mm
Compression Ratio:
7.7:1 (Typical for this era, may vary slightly based on region)
Engine Cooling:
Forced Air Cooling
Ignition:
CDI (Capacitor Discharge Ignition)
Horsepower Estimate:
Approximately 28-32 hp (at crankshaft, unconfirmed exact figure for this specific year)
Torque Estimate:
Approximately 16-18 lb-ft (at crankshaft, unconfirmed exact figure)
Carburetor Model:
Mikuni VM28SS (typical)
Fuel Type:
Unleaded gasoline (91-98 octane recommended)
Fuel Mixture:
Requires 2-stroke oil pre-mix. Recommended ratio: 20:1 (Gasoline:Oil).
Fuel Tank Capacity:
7.0 L (1.85 US gal)
Length:
Approx. 2160 mm (85.0 in)
Width:
Approx. 815 mm (32.1 in)
Height:
Approx. 1250 mm (49.2 in)
Wheelbase:
Approx. 1460 mm (57.5 in)
Ground Clearance:
Approx. 350 mm (13.8 in)
Dry Weight:
Approx. 95 kg (209.4 lbs)
Wet Weight:
Approx. 103 kg (227.1 lbs) (with all fluids)
Safety Rating Description:
Off-road vehicles are not typically subjected to DOT safety ratings. Safety relies on rider skill and proper maintenance.
Braking System:
Front and Rear Drum Brakes. Lever-actuated front, foot-actuated rear.
Chassis Design:
Sturdy steel frame designed for torsional rigidity and impact resistance.
Infotainment Features:
N/A (Performance motocross bike, no infotainment systems).
Driver Assistance Features:
N/A (No electronic rider aids or driver assistance systems).
Connectivity Features:
N/A (No electronic connectivity features).
Oil Change Interval:
Every 10-15 hours of riding, or every 3 months. Check manual for specific recommendations.
Air Filter Cleaning:
Clean after every few rides, or more frequently in dusty conditions. Replace as needed.
Spark Plug Inspection:
Inspect every 10-15 hours. Replace when gap is out of spec or electrode is worn.
Chain Lubrication Adjustment:
Lubricate chain after every wash or ride in wet conditions. Adjust slack every 10-15 hours.
Transmission Oil Type:
Yamalube Gear Oil 10W-30 or equivalent API GL-4 SAE 80.
Transmission Oil Capacity:
0.75 L (0.79 US qt)
Fork Oil Type:
Yamalube Fork Oil G10 or SAE 10W fork oil.
Fork Oil Quantity:
300 ml (10.1 US fl oz) per fork leg.
Premix Oil:
Yamalube 2R or similar high-quality 2-stroke racing oil.
Common Wear Items:
Piston rings, clutch plates, wheel bearings, steering head bearings, swingarm bearings, brake shoes.
Engine Performance Degradation:
Loss of compression due to worn piston/rings, clogged exhaust port, worn reed valves.
Suspension Issues:
Leaking fork seals, worn rear shock damping.
Carburetor Tuning Sensitivity:
Highly sensitive to altitude and temperature changes, requiring regular jetting adjustments.
Yamaha Motorcycles Legacy:
Yamaha has a long and storied history in motorcycle racing, particularly in motocross, with a reputation for innovation and performance.
Yz Series History:
The YZ series has been a cornerstone of Yamaha's motocross lineup since the 1970s, consistently evolving with new technologies and chassis designs.
1980S Yz125 Developments:
The mid-to-late 80s saw significant advancements, including the adoption of the Monocross rear suspension, improved engine tuning (reed valves, exhaust ports), and revised chassis geometry for better handling.
Manufacturing Location:
Japan (Primary manufacturing hub for Yamaha)
Production Period:
Ongoing model line since the 1970s.
Motocross Titles:
The YZ125 platform has historically been a strong contender in national and international motocross championships, though specific wins for the 1988 model year would require historical racing data.
Magazine Reviews Era:
Contemporary reviews often praised its strong engine performance for its class and its nimble handling characteristics.
Emissions Certifications:
N/A for competition off-road vehicles of this era.
