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