1977 Yamaha xs400

Yamaha XS 400

Make Model	Yamaha XS 400
Year	1977 - 78
Engine	Four stroke, 180° parallel twin, SOHC, 2 valves per cylinder
Capacity	392 cc / 23.9 cu-in
Bore x Stroke	69.0 x 52.4 mm
Cooling System	Air cooled
Compression Ratio	9.2:1
Lubrication	Pressure-lubricated wet sump
Induction	2x Mikuni BS32 carburetors
Ignition	Battery ignition - With contact breaker points
Starting	Electric & kick
Max Power	36 hp / 26.8 kW @ 8100 rpm
Max Torque	3.3 kgf-m / 23.8 lb-ft @ 8000 rpm
Clutch	Wet multiplate
Transmission	6 Speed
Final Drive	Chain
Frame	Tubular steel, semi-double cradle
Front Suspension	Telescopic fork
Rear Suspension	Dual shocks swing arm, preload adjustable
Front Brakes	Single disc
Rear Brakes	Single disc
Front Tyre	3.00-18
Rear Tyre	3.50-18
Wheelbase	1364 mm / 53.7 in
Seat Height	780 mm / 30.7 in
Wet Weight	182 kg / 401 lbs
Fuel Capacity	14 Litres / 3.7 US gal

Yamaha have been trying to cater for all tastes and marketing machines with similar capacity in both two-stroke and four-stroke guises in the mid 70s. The XS400 is the company's four-stroke machine in the popular 400 class and is completely different from the RD400 two-stroke which has a much sportier image, even if in reality both bikes are just about equal in performance.

The XS4Oo's nearest relation is the similar-looking XS360, and both have parallel air-cooled twin-cylinder engines driving through six-speed gearboxes.

The single-overhead-camshaft unit is very oversquare with dimensions of 69mm bore by 52mm stroke, and it can rev to 9000rpm, which is quite high for a twin. Unlike the other 400 twins in the same class, the XS does not have counter balance shafts, which means the motor does vibrate more than the opposition, but this is not noticeable above 45oorpm. More important than the bike's 38bhp is the torque produced which peaks at 22lbft at 75oorpm, but stays within 5lbft of that figure right down to 4000. On the road, this means that the Yamaha will pull strongly and evenly over a large speed band.

A top speed of 105mph can be achieved while acceleration over a standing start quarter mile takes a very creditable I4.o.secs. There are single disc brakes at the front to stop the bike which are mounted on attractive alloy wheels which, in turn, help take away some of the bulkiness of the bike's looks. Yamaha have also devised neat paintwork on the tank and side panels which helps break up the lines, again to make the bike appear smaller than its 3621b would otherwise suggest.

The standard of equipment on the middleweight Yamaha is equal to that of many Japanese machines, and betters them with an ingenious indicator system which is worked by a linkage to the speedometer. This means that the winkers stay on for a certain distance which has no bearing on time but just distance travelled.