1977 Yamaha YZ125
Specifications and workshop reference information for the 1977 Yamaha YZ125, including engine, chassis, service data and setup details.
Photo credit:
VMX Re-Creations
– Vintage Yamaha YZ125 restoration
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 | Air-cooled, 2-stroke, single-cylinder |
| Displacement | 123 cc |
| Bore × Stroke | 56.0 mm × 50.0 mm |
| Compression Ratio | ~7.0:1 |
| Maximum Power | ~20 hp |
| Maximum Torque | N/A |
| Carburetor | Mikuni VM32SS |
| Lubrication | Premix |
| Fuel Mix Ratio | 20:1 – 32:1 |
| Ignition | CDI |
| Spark Plug | NGK B8ES |
| Spark Plug Gap | 0.6 – 0.7 mm |
Transmission
| Transmission Type | 5-speed manual |
| Clutch | Wet, multi-plate |
| Primary Reduction | 3.409 |
| Final Reduction | Chain drive |
| Overall Reduction | N/A |
Dimensions
| Overall Length | 2130 mm (approx.) |
| Overall Width | 820 mm (approx.) |
| Overall Height | 1150 mm (approx.) |
| Wheelbase | 1405 mm (approx.) |
| Ground Clearance | 300 mm (approx.) |
| Fuel Tank Capacity | 7.5 L (approx.) |
Chassis
| Frame Type | Double cradle steel frame |
| Caster Angle | N/A |
| Trail | N/A |
| Front Suspension | Telescopic forks |
| Rear Suspension | Monoshock (Monocross) |
| Front Suspension Travel | ~250 mm |
| Rear Suspension Travel | ~270 mm |
Brakes & Wheels
| Front Tire | 2.75-21 |
| Rear Tire | 3.50-18 |
| Front Brake | Drum |
| Rear Brake | Drum |
125cc Other Specs
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