XS1-B Road Test
After making only 2-stroke models for the 15
years since its founding, to the point that
its brand name had become synonymous with 2-strokes,
Yamaha introduced its first 4-stroke engine
on this model, which quickly won a popular following.
The goal of building a “lightweight, slim
and compact big-displacement sports model,”
was achieved by mounting a vertical OHC twin
engine characterized mainly by its slimness
on a slim double cradle frame.
- Overall length x width x height: 2,175mm
x 905mm x 1,115mm
- Weight: 185kg
- Engine-type: Air-cooled 4-stroke OHC 2-cylinder
- Maximum power output: 53ps/7,000rpm
- Maximum torque: 5.5kg-m/6,000rpm
XS1-B 650cc Motorcycle Sport July 1972
Maybe the British have been renowned as the
builders of big vertical twins, maybe they have
(or at least like to think that they have) got
a stranglehold on this sector of the market.
Yamaha's answer has been to market a machine
that hits right at the heart of all that is
dear to the British way of motorcycling.
Naturally they have not been content merely
to copy existing designs. They have introduced
a valve operation by single-chain-driven overhead
camshaft, electric starter, five-speed gearbox
and disc front brake. None of these ideas would
count as revolutionary but, as far as we can
think, only Laverda incorporate them all in
another motorcycle using this engine layout.
The present model, the XS 650, is not Yamaha's
first venture into producing a four-stroke;
two years ago they offered, for the first time,
the XS1. This was basically the same as the
present model except that it lacked a disc front
brake, electric starter. The XS1 engine was,
in fact, a scaled-down version of the Toyota
2000GT car, which was also built by Yamaha engineers.
So you can see that although the Hammatsu company
are famous for making very quick two-strokes
they are not complete novices when it comes
to producing a four-stroke.
The Yamaha is, indeed, somewhat "British"
in concept. It has the same tautness that home
manufacturers often give us, the same clean
good looks and healthy exhaust note. It differs
really only in sophistication (the Japanese
being more so) and a more flamboyant approach
which does not shrink from bright colours. Our
machine, for example, was in orange with black
and yellow stripes on the tank, and bags of
polished alloy and chrome. It most definitely
would not be the machine to buy if one wanted
to pass unnoticed (although the exhaust note
would see to that no matter what colour the
First a look at that comparative innovation
from Yamaha: the four-stroke engine.
The overhead camshaft is driven, Honda style,
by a chain which passes between the cylinders.
At the top end the chain powers a sprocket on
the camshaft which in turn operates the valves
through tappets. Adjustment of the chain is
by tensioner reached from the rear of the cylinders.
The camshaft, with a bearing at each end, has
the dual contact breaker assembly on the righthand
side and the automatic advance and retard, operated
by bob weights, on the left. The shaft is hollow
with a governor rod passing through from end
to end and responsible for the necessary degree
of advance or retard. The whole camshaft operation
is a simple one and it would be a pity if riders
were to shy away from it because of the mystique
that used to be attached to such a system. Honda
have long since blown that sky high.
The 360° crankshaft, has four roller bearings,
two at each end and two in the middle (one either
side of the camshaft sprocket). On the righthand
end of the shaft there is the straight-cut spur
gear primary drive. Outside this gear is another
smaller gear driving the trochoidal rotary oil
pump. Lubricant is carried in the sump and delivered
under pressure to main bearings, big end, transmission
main axle, clutch bearing, shift fork guide
bar and rocker arms. The crankshaft, small ends,
cam chain, pistons and bore and primary gears
are splash lubricated. A re-usable oil filter
is located in the front of the righthand timing
case with a spring-loaded ball valve in the
locking bolt to act as a by-pass, should the
filter become clogged. At the other end of the
crankshaft is a Hitachi alternator. Twin coils
are mounted under the petrol tank, and the regulator
is under the seat. The 12v battery has a rating
of 5.5 a/h.
The 653 c.c. engine produces a claimed 53 b.h.p.
at 7,000 r.p.m. It has a compression ratio
of 8.7 to 1 with a slightly oversquare dimensions
of 75mm bore, 74mm stroke. One interesting piece
of information to emerge from our research is
that the engine unit weighs 135 Ib.
Carburettors are of the constant vacuum Solex
type made by Mikuni, with a 30.6mm choke. The
Japanese seem to have made a most successful
job of producing this type of carburettor
and the units fitted to the test machine behaved
very well indeed most of the time, although
they had a slight tendency to allow the engine
to "die" unexpectedly. That was when
we really appreciated the electric starter!
Yamaha have made a fair job 'of adding an electric
starter unobtru- sively to an existing design,
for they have located it underneath the gearbox
and taken the drive, rather torturously, by
gear and shaft, direct to the crankshaft. Engagement
is by "Bendix" gear. To turn over
a powerful big twin engine, as we have often
remarked in the past, requires quite a
swing and to pass this task on to an electric
starter motor producing, initially, 135 amps
could give the battery a very hard life. The
problem has been overcome, ingeniously, by,
coupling the starter motor contact to a decompressor
valve so that considerable assistance is given
to the starter motor when it most needs it.
It worked very well but sounded, on occasion,
a trifle wheezy, especially if the motor was
a little slow to fire. The logical place to
mount the decompressor lever-cum-starter switch
seemed, to us, to be in the traditional position
under the clutch lever but Yamaha have chosen
to place it below the throttle. As one also
needed to operate the throttle at the same time
as the starter we found it expedient to use
the left hand as well.
The frame is of double cradle type with the,
now, almost universal Ceraini-type front forks.
The travel in these forks ough^ to be just over
5 in. but ours were distinctly non-standard
in this respect and .at times seemed to have
less movement than a set of overinflated Oleomatics!
Upon returning the machine to the concessionaires
we gathered that Yamaha were doing a little
experimenting with heavier oils in the forks
of the test model, and we were guinea pigs,
so to speak. One pothole in central London was
severe enough to knock the breath out of me.
It was a situation that was not helped by very
stiff rear suspension and a seat that appeared
to have very little padding on "its"
base even before one sat on it! One doesn't
exactly float along on a cushion of air on this
machine. The seat hinges to reveal the tool
tray and the battery.
Tyres on the test machine were Japanese Dunlop,
4.00 x 18in rear, 3.50 x Win front. There was
a considerable amount of wet weather riding
done during our period of ownership and the
only time we felt any concern on roadholding
was on one occasion when, with the machine banked
over for a slow corner, the power came in with
a bit of a rush. The machine momentarily stepped
sideways but, as the power was eased, quickly
settled back on to line. We were happy enough
with the tyres. Brakes; disc front and drum
rear. We have read other tests where the Yamaha
disc has been criticized for lack of sensivity
(feedback was the "in" term, which
we would rather not use). We would say this
was one of the best disc brakes we have ever
tried—effective, efficient and reliable.
Its only vice was a tendency to squeal
occasionally. So full marks for the brakes.
That this machine was never really intended
as a serious contender in this country can be
seen from the handlebars. The highest, widest
and possibly handsomest bars you ever saw.
Fine for town use or up to 70 m.p.h. but for
real highspeed touring, agony! The instrumentation
is clean and easy to read although the speedometer
and tachometer both suffer from white light
reflecting off the shell at night. The two are
illuminated with a very restful green light
but this effect was spoiled for us by all this
ex-teraneous light. The light controls are what
one might almost term "standard Japanese".
The left-hand operated dip-switch and main switch
are side by side with the dip nearest the thumb.
Below that the "left-to-right" flasher
switch and below that the barely adequate horn's.
Yamaha clearly believe in as much illumination
as the generator allows for they have opted
for a slightly above average 27w flasher bulb.
Regrettably, it is still not really good enough
for daytime use. The stop light is 27w, and
the tail light 8w, again slightly above average,
and the headlight a whacking 50/40w. It was
without doubt one of the best of its type
we have tried and night driving behind this
kind of light is a real pleasure.
The bulb is Stanley but not the more usual
offset bayonet; it is in fact American pre-focus.
We think that one or two owners of other large-capacity
machines might well be wondering how to fit
the complete unit. A parking/driving light is
operated by a separate switch in the headlamp.
Normally we are reluctant to trust small
parking lights for night riding but occasionally,
around dusk, the 40w dipped beam became something
of an embarrassment. The on/off switch, next
to the right thumb, was all too frequently accidentally
knocked to the "off" position, stopping
everything. It is all very well reeling off
sheets of technical specifications but the question
prospective buyers are going to ask is, "Is
it better than a Bonneville, and if so how?".
Perhaps we were expecting too much of the machine.
We really did expect the Yamaha company
to have overcome the one real problem that
vertical twin owners never tire of complaining
about—vibration. It is not an insurmountable
problem. Norton have at least harnessed
it and the 450 Honda seemed to be well on the
way to beating the bug completely. Perhaps
it has beaten it by now but, as one never sees
one of these excellent machines in this
country, it is difficult to tell.
Sad to say then that the Yamaha has the old
familiar bogey of vibration. True it has been
smoothed out in places but when one is accelerating
in the gears or pushing the willing 650 along
in excess of 4,000 r.p.m. the bike does vibra;e.
The footrests are the first to pass on the mes-isage,
then the seat of the pants and finally, when
things are really buzzing, the handlebar grips.
Please do not get the idea that the thing is
shaking itself apart. It isn't but it is not
as smooth as a three-or four-cylinder machine.
It is strange that in some respects the vibration
does not show at all. The mirrors, for example
(and the handlebars are not rubber mounted),
never for a moment lost their sharpness of image.
We have always felt that twin mirrors, mounted
as they were on the 650, look a little "sissy"
but there can be no faulting their effectiveness.
A car 50 yards behind could be seen in both
mirrors, clearly, and so could both kerbs. When
one considers that Yamaha declined to import
the little trail bike into this country on account
of its exhaust noise one wonders just how noisy
it was. This machine, too, is really quite raucous
and must have caused a little head-scratching
before it was finally offered for sale over
here. The silencers are of the fat cone type
and appeared to play a small part in muting
the exhaust note. Music to some but ammunition
to our enemies. The exhaust pipes, while we
are in that area, showed not a trace of blueing.
First-gear engagement was always silent and,
generally speaking, the gearbox was as light
and smooth as one could wish. The exception
was if one was a little slow changing down when
bulked by traffic. Then it showed a marked reluctance
to travel quickly through, say, second and third
and it was easy to be caught out in too high
a gear. The reward for this was a sharp kick
from the transmission, a reminder that
underneath was a potent •• motor
that would not be abused. In other respects
the engine was more than docile. If one eased
the throttle back it was quite possible to burble
along at 1,000 r.p.m. in top gear at just under
20 m.p.h. It would not, it is true, accelerate
without assistance from the gearbox from
that speed but that is, perhaps, asking too
The big virtue of an engine design such as
this is its deep, biting response from low down.
Torque. The Yamaha has it by the bucketful.
It showed in many ways. Perhaps one would be
pottering along in traffic at 35/40 m.p.h. (indicated,
the speedometer was at least 10 per cent fast
through the range). The chance to overtake would
present itself and a flick of the throttle was
sufficient to send the 650 soaring up to the
70s without a thought of using the gearbox.
At the other end of the range, if one was pressing
on just a little and was bulked at 70 m.p.h.
a drop into fourth gave the machine just that
little extra kick and in no time at all 90 was
showing and fifth could be re-engaged. This
is one of the great benefits of a five-speed
box. With the normal four-speed box one is reluctant
to hold third at high speed for as long as the
motor is usually sounding over busy, but with
the extra ratio to play with the sensible engineer
will have provided a ratio just below normal
top to give that little bonus. Yamaha have done
just this and the result is most acceptable.
The Yamaha XS 650 is no lightweight, turning
the scales at 427 Ib, but the electric
starter accounts for a little of this and the
weight was never really noticeable the large
bars giving one more than enough pull if traffic
threading was in hand. At the top of the range
the machine did not behave quite as we
expected it to. It coped admirably up to the
legal limit and behaved just as a well
designed vertical twin should. Then, while being
pushed through fast, bumpy bends, it would show
a tendency to weave a little. We are in
something of a dilemma over this for we
understand that a previous tester threw
it down the road one wet day (we are not gloating,
it could just as easily happen to us). Yamaha
say they suspect a slight twist in the frame,
citing the machine's reluctance to steer hands
off since the accident. This may well be so,
and how can one criticize a feature that may
not be typical of the model? Rest assured that
we will pursue this theme if the opportunity
arises to try another XS 650.
Claimed top speed of the big Yamaha is 115-plus.
It seems to us to be a little on the optimistic
side and our suggestion is that 105 is nearer
the mark. More important, in our view,
is the way it reaches its maximum. There is
no flattening off in acceleration until the
speedometer needle is past the three-figure
mark and even if one chooses to accelerate from
40 m.p.h. in top gear the magic 100 still appears
in quick time. The XS 650 is, without doubt,
a fast roadburner but this side of its nature
is let down by a 2l/2 gallon petrol tank. We
ask you, 2% gallons! If the machine is ridden
really hard 45 m.p.g. or less can be expected,
giving it a range of just over 100 miles. With
our new motorways that means stopping for petrol
every 80 minutes or so, allowing for service
station frequency and an adequate reserve.
The exhaust note was more than a little embarrasing
in town and consequently we kept a careful throttle
hand. Every cloud has its silver lining, though,
and under these conditions we found that the
machine would return over 60 m.p.g. We would
prefer to spend our petrol though rather than
merely let it slowly drain away.
We find ourselves in the position of worrying
that we may have been a little hard on this
big 'un from Yamaha. You see, it is as least
as good as most others in its class and offers
a degree of sophistication rare in home-produced
machinery at roughly the same price (£650).
Trouble is, we expected much more. We imagined
that Yamaha would not have considered making
a vertical twin unless it could beat the pants
off long-established British rivals. Frankly
it can't. It is as quick as some, has disc brakes
and electric starter and first-class lighting
but it wasn't the most comfortable machine that
we have ever tested and vibrated, if anything,
slightly more than the Bonniville we tried last
year. Viewing it as a direct rival to the British
big bike brigade, the question comes down to
sophistication v. experience with a possible
bonus going to the home industry when it comes
to cost and availability of spares. The XS 650
Yamaha is a bright and cheerful addition to
the market and certainly has not disgraced
itself but we cannot help feeling that Yamaha's
heart is really in the world of two-strokes.
If they are going to score heavily in the big
bike league it will be with the water-cooled
four-cylinder two-stroke they introduced in
Tokyo earlier this year.
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