| MODEL | YAMAHA XS 400 1979 |
| Year | 1979 |
| Engine Type | Four stroke, 180 degree parallel twin, SOHC, 2 valves per cylinder |
| Displacement / Capacity | 392 cc / 23.9 cu in |
| Bore X Stroke | 69.0 x 52.4 mm |
| Compression Ratio | 9.2:1 |
| Cooling System | Air cooled |
| Max Power | 26.8 kW / 36 hp @ 8100 rpm |
| Max Torque | 3.3 kgf-m / 23.8 lb-ft @ 8000 rpm |
| Ignition | Battery ignition, contact breaker points |
| Induction | 2x Mikuni BS32 carburettors |
| Start System | Electric & kick |
| TRANSMISSION SPECS | |
| Lubrication | Pressure-lubricated wet sump |
| Gear Box | 6 speed |
| Clutch | Wet multiplate |
| Final Drive | Chain |
| CHASSIS SPECS | |
| Frame | Tubular steel, semi-double cradle |
| Front Suspension | Telescopic fork |
| Rear Suspension | Dual shocks, swing arm, preload adjustable |
| Front Brakes | Single disc |
| Rear Brakes | — |
| DIMENSION SPECS | |
| Overall Length | — |
| Overall Width | — |
| Overall Height | — |
| Seat Height | 780 mm / 30.7 in |
| Wheelbase | 1364 mm / 53.7 in |
| Ground Clearance | — |
| Dry Weight | — |
| Wet Weight | 182 kg / 401 lb |
| WHEEL SPECS | |
| Front Tyre | 3.00-18 |
| Rear Tyre | 3.50-18 |
| FUEL SYSTEM | |
| Fuel Capacity | 14 Litres / 3.7 US gal |
| Fuel Consumption | — |
| Top Speed | — |
The 1979 model-year continuation of Yamaha's SOHC 400 parallel twin, carried over mechanically unchanged from the first two years on the figures published. It remained the relaxed, torquey, six-speed budget twin with electric and kick starting.
