1984 Yamaha YZ125
Specifications and workshop reference information for the 1984 Yamaha YZ125, including engine, chassis, service data and setup details.
Note: Specs are compiled from factory data, manuals and owner feedback. Bikes vary — if yours is different, jump into the forum and share it.
General Specifications
| Engine Type | Liquid-cooled 2-stroke single, reed valve, YPVS |
| Displacement | 123 cc |
| Bore × Stroke | 56.0 × 50.0 mm |
| Compression Ratio | ~8.7–10.5:1 |
| Maximum Power | ~31–33 hp |
| Maximum Torque | N/A |
| Carburetor | Mikuni VM34SS |
| Lubrication | Premix |
| Fuel Mix Ratio | ~32:1 |
| Ignition | CDI magneto |
| Spark Plug | NGK BR9EG |
| Spark Plug Gap | 0.5–0.6 mm |
Transmission
| Transmission Type | 6-speed constant mesh |
| Clutch | Wet multi-plate |
| Primary Reduction | ~3.409 |
| Final Reduction | ~3.714 (13T / 48T) |
| Overall Reduction | N/A |
Dimensions
| Overall Length | ~2145 mm |
| Overall Width | ~820 mm |
| Overall Height | ~1240 mm |
| Wheelbase | ~1445 mm |
| Ground Clearance | ~340 mm |
| Fuel Tank Capacity | ~8.0 L |
Chassis
| Frame Type | Steel single downtube |
| Caster Angle | ~27.5° |
| Trail | ~115 mm |
| Front Suspension | Kayaba telescopic forks (improved damping) |
| Rear Suspension | Monocross rising-rate linkage |
| Front Suspension Travel | ~300 mm |
| Rear Suspension Travel | ~315 mm |
Brakes & Wheels
| Front Tire | 3.00-21 |
| Rear Tire | 4.50-18 |
| Front Brake | Drum |
| Rear Brake | Drum |
125cc Other Specs
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