The 1986 Yamaha YZ 125 is a high-performance motocross motorcycle featuring a liquid-cooled 2-stroke 125cc engine, 6-speed transmission, front and rear suspension systems, disc brakes, and competition-oriented chassis design. This manual covers essential information for maintenance, operation, troubleshooting, and specifications to ensure optimal performance and longevity of your motorcycle.
Key components: Liquid-cooled 2-stroke engine, 6-speed transmission, front telescopic fork suspension, rear monoshock suspension, front and rear disc brakes, aluminum frame.
| Feature | Description |
|---|---|
| Engine Type | Liquid-cooled 2-stroke single cylinder |
| Displacement | 125cc |
| Transmission | 6-speed constant mesh |
| Front Suspension | Telescopic fork, air-adjustable |
| Rear Suspension | Monoshock, fully adjustable |
| Front Brake | Single disc, hydraulic |
| Rear Brake | Single disc, hydraulic |
| Frame Type | Aluminum semi-double cradle |
| Fuel Capacity | 2.1 gallons (8 liters) |
| Dry Weight | 198 lbs (90 kg) |
Unpack and inspect all components. Ensure proper assembly before operation.
WARNING! Motorcycle is heavy; use proper lifting techniques. Ensure all fasteners are tightened to specified torque values.
Complete initial setup procedures before first ride.
CAUTION! Always wear proper safety gear. Break in engine gradually during first hours of operation.
Familiarize yourself with all controls before riding.
Left Handlebar: Clutch lever, horn button, high/low beam switch, turn signal switch.
Right Handlebar: Front brake lever, throttle grip, engine stop switch, start button.
Foot Controls: Gear shift lever (left), rear brake pedal (right).
Starting Procedure: Turn fuel valve ON, pull choke (cold engine), kick start firmly. Allow warm-up before riding.
Regular maintenance ensures optimal performance and safety.
Tip: Keep maintenance log to track service intervals and repairs.
2-stroke engine requires specific maintenance procedures.
WARNING! Engine components become extremely hot during operation. Allow sufficient cooling time before servicing.
Proper suspension setup and brake maintenance crucial for control and safety.
Front Suspension: Oil capacity 435cc per leg, spring preload adjustable. Rear Suspension: Spring preload, compression and rebound damping adjustable. Brakes: Use DOT 4 brake fluid, bleed system annually or as needed.
Proper storage prevents damage and maintains motorcycle condition.
Clean motorcycle thoroughly after each ride. For long-term storage: Drain fuel system, remove battery, lubricate all moving parts, store in dry location covered with breathable material.
CAUTION! Do not use high-pressure water spray on bearings or electrical components.
This motorcycle is designed for closed-course competition use only. Not legal for street use in most jurisdictions. Yamaha Motor Corporation, USA. For technical support and parts, contact authorized Yamaha dealers or visit www.yamaha-motor.com.
| Symptom | Possible Cause | Corrective Action |
|---|---|---|
| Hard starting | Fouled plug, improper fuel mix | Replace spark plug, ensure proper 32:1 fuel/oil ratio. |
| Poor performance | Clogged air filter, carb issues | Clean air filter, check carburetor jetting and settings. |
| Overheating | Low coolant, lean mixture | Check coolant level, inspect for leaks, check jetting. |
| Transmission issues | Worn clutch, improper oil | Inspect clutch plates, use recommended transmission oil. |
| Brake problems | Air in system, worn pads | Bleed brake system, replace pads if below minimum thickness. |
Service Intervals: Oil change every 10 hours, piston inspection every 20-30 hours.
Support: Contact authorized Yamaha dealer for technical assistance and genuine parts.