From Yamaha Wiki
The Yamaha XS250, XS360, and XS400 are all nearly identical variations of the same XS400 motorcycle platform made by Yamaha from 1977 to 1982. Additionally, later bikes also received Special, Special II, and Heritage badges denoting "factory custom" features.
The XS400 featured a four-stroke, air-cooled, overhead-cam engine that is commonly called a "parallel twin", though while the twin cylinders are indeed parallel the two pistons are offset 180 degrees of crankshaft rotation -- this arrangement greatly reduces linear vibration at the cost of some axial vibration. The 250CC engine produced 27HP @ 9,500RPM, the 360CC engine 34HP @ 8,500RPM, and the 400CC 36HP @ 9,000RPM.
The XS400 was equipped with a 6-speed transmission, chain drive, tachometer, self-canceling turn signals, both electric and kick starters, adjustable rear shock absorbers, center stand, and an automatic fuel petcock. Early and economy models came with spoked wheels and drum brakes, while later and upgraded models received cast alloy wheels and hydraulic disc brakes. Later models also upgraded the early mechanical points ignition system to a modern solid state electronic system.
As is customary, the number in the model name indicates the engine displacement. Aside from displacement, the 250CC, 360CC, and 400CC variants were mostly identical except for some economy-minded XS250s and XS360s which omitted the electric starter and self-canceling turn signals. The upgraded Special and Heritage trim levels included styling changes such as stepped seats, megaphone-style exhaust pipes, and swept-back handlebars.
Weight is approximately 160kg (360lbs), and fuel capacity about 11l (3g).