RD 400

1978 Yamaha RD 400 Technical Analysis & Specification Breakdown

Built around Yamaha's classic motorcycle platform, the 1978 Yamaha RD 400 relies on a 399 cc (24.4 cu in) air-cooled twin, two-stroke powerplant. In factory specification, peak output is rated at 43 HP (31.4 kW) at 7,500 rpm, transferring power to the rear wheel through a 6-speed gearbox and chain final drive. With a specific output of 107.8 HP per liter, the engine character is reflecting a performance-oriented street tune that balances strong mid-range pull with an energetic top-end rush.

On the scales, the RD 400 measures 175 kg (386 lbs) wet (curb), translating to a power-to-weight ratio of 0.25 HP/kg (4.07 kg per horsepower). The 16.5-liter (4.4 US gal) fuel tank supports practical everyday commuting and weekend road stints, while factory top speed is listed at 175 km/h (109 mph).

Within MotoLibrary's Yamaha archive, this model family spans 2 indexed model years from 1978 to 1979, allowing buyers to track year-over-year changes in emissions tuning, weight and equipment.