| MODEL | YAMAHA SR 400 1978 - 1980 |
| Year | 1978 - 1980 |
| Engine Type | Four stroke, single cylinder, SOHC, 2 valves per cylinder |
| Displacement / Capacity | 399 cc / 24.3 cu in |
| Bore X Stroke | 87 x 67.2 mm |
| Compression Ratio | 8.5:1 |
| Cooling System | Air cooled |
| Max Power | 16.7 kW / 22.93 hp @ 6500 rpm |
| Max Torque | 27.4 Nm / 20.2 lb-ft @ 3000 rpm |
| Ignition | CDI |
| Induction | VM32 carburettor |
| Start System | Kick |
| TRANSMISSION SPECS | |
| Lubrication | Wet sump |
| Gear Box | 5 speed |
| Clutch | Wet, multiple disc |
| Final Drive | Chain |
| CHASSIS SPECS | |
| Frame | Steel double cradle |
| Front Suspension | 35 mm telescopic fork, 150 mm / 5.9 in travel |
| Rear Suspension | Dual shocks, 5-way adjustable preload, 105 mm / 4.1 in travel |
| Front Brakes | Single disc |
| Rear Brakes | Drum |
| DIMENSION SPECS | |
| Overall Length | — |
| Overall Width | — |
| Overall Height | — |
| Seat Height | 790 mm / 30.9 in |
| Wheelbase | 1410 mm / 55.5 in |
| Ground Clearance | 130 mm / 5.1 in |
| Dry Weight | — |
| Wet Weight | 174 kg / 384 lbs |
| WHEEL SPECS | |
| Front Tyre | 3.50-19 |
| Rear Tyre | 4.00-18 |
| FUEL SYSTEM | |
| Fuel Capacity | 12 Litres / 3.2 US gal |
| Fuel Consumption | — |
| Top Speed | — |
The original SR400, launched in Japan in 1978 alongside the SR500 as a kick-start-only retro single with a shorter-stroke engine that kept it under the 400 cc licence class. It carried a front disc brake, rear drum and a steel double-cradle frame with a decompression lever and sight glass for easier starting. Simple, light and torquey rather than fast.
