Yamaha XS 400

 

 

 

Make Model

Yamaha XS 400

Year

1977 - 78

Engine

Four stroke, parallel twin cylinder, 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

Induction

2X Mikuni BS32 carburetors

Ignition 

Battery ignition - With contact breaker points 
Starting Electric & kick

Max Power

38 hp / 27 kW @ 8800 rpm

Max Torque

3,3 kgf-m / 23.8 lb-ft @ 8000 rpm

Transmission

6 Speed 
Final Drive Chain

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

3.75-18

Wet Weight

182 kg / 401 lbs

Fuel Capacity 

17 Litres / 4.5 US gal

Consumption Average

60 mpg

Standing ¼ Mile  

14.3 sec

Top Speed

105 mph

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 either end 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.