At the heart of the 1979 Yamaha XS 400 classic motorcycle, Yamaha relies on a 392 cc (23.9 cu in) air-cooled twin, four-stroke powerplant. In factory specification, peak output is rated at 27 HP (19.7 kW) at 7,000 rpm while maximum torque reaches 31.2 Nm (23 lb-ft) at 6,000 rpm, transferring power to the rear wheel through a 6-speed gearbox and chain final drive. With a specific output of 68.9 HP per liter and a 1,000 rpm working window between peak torque (6,000 rpm) and peak power (7,000 rpm), the engine character is indicating a tractable, stress-free state of tune focused on everyday usability and broad torque delivery.
On the scales, the XS 400 measures 182 kg (401 lbs) wet (curb), translating to a power-to-weight ratio of 0.15 HP/kg (6.74 kg per horsepower). Rider ergonomics and chassis geometry center around a 780 mm (30.7 in) seat height — offering a neutral standover height that accommodates most average-inseam riders without sacrificing cornering clearance, combined with a 1,364 mm (53.7 in) wheelbase engineered for quick, flickable steering geometry. The 17-liter (4.5 US gal) fuel tank supports practical everyday commuting and weekend road stints, while factory top speed is listed at 140 km/h (87 mph).
Within MotoLibrary's Yamaha archive, this model family spans 5 indexed model years from 1978 to 1982, allowing buyers to track year-over-year changes in emissions tuning, weight and equipment.
Specific Output
68.9 HP/L
Power-to-Weight
0.15 HP/kg (6.74 kg/HP)
Power Band Window
6,000–7,000 rpm
Standover Height
780 mm (30.7 in)
Engine
Displacement392.0 ccm (23.92 cubic inches)
Engine TypeTwin, four-stroke
Engine DetailsTwin, four-stroke
Power27.0 HP (19.7 kW)) @ 7000 RPM
Torque31.2 Nm (3.2 kgf-m or 23.0 ft.lbs) @ 6000 RPM
Compression9.2:1
Bore x Stroke69.0 x 52.4 mm (2.7 x 2.1 inches)
Valves/Cylinder2
Fuel SystemInjection. 2 x Mikuni BS32
Fuel ControlOverhead Cams (OHC)
IgnitionBattery ignition - With contact breaker points
Use this page to compare this motorcycle by its real specifications, not only by model name. Focus on the details that affect fit, comfort, handling, range and ownership.
Power
Compare engine output with similar motorcycles if acceleration, highway use or two-up riding matters.
Torque
Torque is useful for judging real-world pull, especially for touring, commuting and loaded riding.
Seat Height
Check the seat height against your inseam and riding posture before choosing a motorcycle.
Weight
Compare weight carefully because it affects low-speed handling, parking and confidence.
Fuel Capacity
Fuel capacity helps estimate touring range and how often you may need to stop.
Brakes
Brake setup is worth comparing if you ride in traffic, mountains or with a passenger.
Suspension
Suspension details can matter for comfort, road feel and long-distance riding.
Transmission
Transmission and final drive affect maintenance, smoothness and everyday usability.
