XS 400

1978 Yamaha XS 400 Technical Analysis & Specification Breakdown

Built around Yamaha's naked motorcycle platform, the 1978 Yamaha XS 400 pairs a 392 cc (23.9 cu in) air-cooled twin, four-stroke architecture with road-focused gearing. In factory specification, peak output is rated at 27 HP (19.7 kW) at 7,000 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, 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). 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.