Market Position:
The Yamaha TZ125 G1 was a highly competitive 125cc two-stroke racing motorcycle, a staple in track racing series and a platform for aspiring professional racers. This manual targets owners and mechanics involved in maintaining and preparing these specialized machines for competition or performance riding.
Competitive Analysis:
In its era, the TZ125 competed against other premier 125cc racing machines from manufacturers like Aprilia, Honda, and Cagiva. Yamaha's TZ series was renowned for its potent engines and excellent chassis dynamics, making a comprehensive service manual essential for maximizing performance.
Key Features:
Comprehensive 'nut and bolt' coverage, hundreds of pages, detailed illustrations, search functionality, step-by-step repair guidance, factory-trained technician knowledge transfer.
Engine System:
Detailed diagnosis, disassembly, inspection, repair, and reassembly of the 125cc two-stroke engine, including carburetor, ignition, cooling (if applicable), and exhaust systems.
Transmission Clutch System:
Complete guide to transmission operation, maintenance, clutch service, gear inspection, and lubrication.
Chassis Frame Suspension:
Includes fork service, shock absorber adjustment and overhaul, swingarm maintenance, and frame integrity checks.
Braking System:
Disc brake system maintenance, caliper overhaul, fluid replacement, and pad inspection.
Electrical System:
Wiring diagrams, component testing, lighting, ignition system troubleshooting, and battery service.
Fuel System:
Carburetor tuning, jetting, cleaning, fuel line inspection, and fuel tank maintenance.
Cooling System:
Details on any liquid cooling systems, including radiator, hoses, and coolant specifications.
Exhaust System:
Exhaust pipe and silencer maintenance, checking for leaks, and performance tuning considerations.
Wheel Tire System:
Wheel bearing service, tire pressure recommendations, and wheel installation.
Bodywork Fairings:
Removal and installation of fairings, seat, and other body panels.
Routine Maintenance:
Oil changes (if applicable to gearbox/clutch), chain adjustment, air filter cleaning/replacement, spark plug replacement, brake fluid flush, coolant checks.
Troubleshooting:
Step-by-step diagnostic procedures for common and uncommon issues, including starting problems, performance issues, and electrical faults.
Engine Rebuilds:
Complete engine disassembly, piston, cylinder, crankshaft, and bearing inspection and replacement procedures.
Transmission Overhaul:
Detailed steps for transmission disassembly, gear inspection, shaft replacement, and reassembly.
Suspension Servicing:
Fork oil replacement, seal replacement, and rear shock absorber maintenance.
Brake System Repair:
Calibrating brakes, replacing brake pads and discs, bleeding the brake system.
Carburetor Adjustment Rebuild:
Jetting information, float bowl adjustment, idle speed settings, and full carburetor rebuild instructions.
Electrical Diagnostics:
Using multimeters to test components, diagnosing ignition system faults, and tracing wiring issues.
Wiring Diagrams:
Clear and detailed wiring schematics for all electrical systems.
Depth:
Factory-level repair and diagnostic information suitable for experienced mechanics and dedicated enthusiasts aiming for complete restoration and maintenance.
Engine Type:
125cc, Liquid-Cooled, Two-Stroke, Single-Cylinder
Bore X Stroke:
Specifications typically found in manual, e.g., 56.0 x 50.7 mm (typical for TZ125).
Compression Ratio:
Specifications typically found in manual, e.g., 8.0:1 to 10.0:1 (varies with tuning).
Ignition System:
CDI (Capacitor Discharge Ignition)
Carburetion:
Single Carburetor, typically Mikuni VM series (e.g., VM28).
Horsepower Output:
Approx. 35-40 HP (stock, varies with tuning and class regulations).
Torque Output:
Specifications typically found in manual.
Fuel Type:
Unleaded gasoline with 2-stroke oil premix (typically 32:1 or 40:1 ratio).
Fuel Tank Capacity:
Specifications typically found in manual, e.g., 8-10 liters.
Engine Top End Rebuild:
Typically recommended every 20-40 hours of racing, or as dictated by performance degradation.
Spark Plug Replacement:
Regularly, based on plug condition, often after every few race weekends.
Chain Lubrication Adjustment:
Before every ride/race.
Brake Fluid Flush:
Annually or as needed, especially after track use.
Engine Oil:
High-quality 2-stroke racing oil, specified by Yamaha or preferred by the rider/mechanic (e.g., Motul, Castrol).
Gearbox Oil:
Yamaha recommends specific mineral or synthetic gearbox oil for 2-stroke transmissions (e.g., SAE 80W or 90).
Coolant:
If liquid-cooled, a mixture of distilled water and appropriate antifreeze/coolant for racing applications.
Brake Fluid:
DOT 4 or DOT 5.1 racing brake fluid, depending on system requirements.
Known Issues:
Typical for high-strung 2-stroke racing engines: piston ring wear, cylinder scoring, crank seal leaks, clutch wear due to aggressive use. The manual provides procedures to diagnose and rectify these.
