1978 Yamaha YZ250
Specifications, manuals and workshop reference information.
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
Note: Power and torque figures are based on period rear wheel dyno testing (Motorcyclist Magazine, 1978) and may differ from factory claimed output.
Source: Period road test (Motorcyclist Magazine, April 1978)
| Engine Type | Air-cooled, two-stroke, reed-valve single |
| Displacement | 246 cc |
| Bore × Stroke | 70 × 64 mm |
| Compression Ratio | 7.3 : 1 (corrected) |
| Maximum Power | 31.28 hp @ 8000 rpm (rear wheel dyno) |
| Maximum Torque | 20.75 lb-ft (28.1 Nm) @ 7500 rpm |
| Carburetor | Mikuni VM38SS |
| Lubrication | Premix (oil in fuel) |
| Fuel Mix Ratio | 20 : 1 |
| Ignition | CDI magneto |
| Spark Plug | Champion N-2G |
| Spark Plug Gap | 0.46 – 0.58 mm |
Transmission
| Transmission Type | Constant mesh, 6-speed |
| Clutch | Wet multi-plate |
| Primary Reduction | 2.608 |
| Final Reduction | 3.846 (13T / 50T) |
| Overall Reduction | Not specified |
Dimensions
| Overall Length | 2145 mm |
| Overall Width | 910 mm |
| Overall Height | 1180 mm |
| Wheelbase | 1458 mm |
| Ground Clearance | 304 mm |
| Seat Height | 952 mm |
| Fuel Tank Capacity | 7.6 L |
| Weight (wet) | 107 kg |
Chassis
| Frame Type | Tubular steel semi double cradle |
| Caster Angle | 30°30' |
| Trail | 134 mm |
| Front Suspension | Telescopic fork |
| Rear Suspension | Monoshock (Yamaha Monocross) |
| Front Suspension Travel | 250 mm (9.8 in) |
| Rear Suspension Travel | 250 mm (9.8 in) |
Brakes & Wheels
| Front Tire | 3.00-21 |
| Rear Tire | 4.50-18 |
| Front Brake | Drum, 130 mm |
| Rear Brake | Drum, 160 mm |
250cc Other Specs
Community
VMX Owners Forum
Discuss vintage motocross bikes, restorations, tuning and riding.