Air cooled, four stroke, single cylinder, SOHC,
Bore x Stroke
73.5 x 56.5 mm
34mm Mikuni carb
Electronically / electric
20 hp @ 7700 rpm
13.7 ft-lb @ 7000 rpm
5 Speed / chain
32mm Telescopic forks
Dual shock 5-way preload adjustment.
The styling approach of Yamaha's
most recent street offerings has taken a turn away from the
conventional. There was a time when all bikes were created equal
i.e. RD250, RD350 etc, but that changed when Yamaha decided to do
some trailblazing by chopperising their more popular road equipment.
The first "revised" model to
reach Australian shores was the Yamaha XS650SF, (TWO WHEELS January
1979) — a high-bar, low-seat version of the ever-popular 650 twin.
Following that came mildly chopperised XS400s, 750s and 1100s. Their
most recent offering retains the style of those former machines but
combines several lessons learnt from past experience.
The SR250H is quite a mixed design. Yamaha has tried to capitalise
on the success of the SR500 theme, i.e. design a dirt four stroke
single and turn it into a roadgoing machine. The demand for a road
single was very strong once XT owners realised their dirt bike
almost did a better job there than on the dirt.
This was obvious from the number
of pseudo-roadgoing XTs appearing with smooth tyres and flat bars.
It's surprising Suzuki didn't realise the potential and convert
their SP370 to street trim also, but that's another story.
Yamaha has designed a first-class 250 cm3 single trailster and
without hesitation, re-employed the engine and frame in a roadster
at the same time. An added advantage is the fact that the laid-back
styling may increase the appeal of the machine to non-bikers.
Economics also played a major role in the design of the 250 and, all
factors considered, the machine is very attractively priced and
quite cheap to run.
But, best of all - just like the
650SF, the SR250H looks just a little bit butch.
Engine and performance In a similar fashion to the XT/SR500 Yamaha
series, the SR250 shares most of is engine and frame design with its
dirt bike counterpart. The obvious visual differences are the lack
of matt black engine enamel and the addition of low slung megaphone
style exhaust, but engine changes go deeper than that.
Internally the SR looks very
similar to the XT, with a bore and stroke of 73.5mm and 56.5mm
respectively giving a 239 cm3 displacement. The engine is decidedly
oversquare (by about 30%) yet gives very usable low £peed torque.
Compression ratio is a moderate 8.9:1. At the bottom end, a built-up
crankshaft runs in single row deep groove ball bearings whilst the
big end of the connecting rod wears a needle roller bearing.
Cylinder head design is quite
conventional with only two valves operated by a chain drive from the
main crank. To improve efficiency and reduce friction, the single
overhead camshaft sits in a set of deep groove ball bearings instead
of the usual bushed bearings or plain alloy. Engine vibration is not
too bad. Yamaha uses a gear driven counter balancer which works
efficiently at low rpm but not so well towards the high end.
Noise level is also well taken
care of and the SR250 is extremely quiet for a
bike with such a short exhaust pipe.
Further major changes include a larger carburettor. Yamaha has used
a 34mm constant velocity unit rather than the slide/needle 28mm
affair fitted to the XT. Throttle response with this carb is good
and the change shows markedly in the reduced fuel consumption. In
line with the totally uncomplicated feel of the SR, Yamaha has
installed an electric starter and disposed of the kick mechanism
altogether (what a good idea for the XT). This modification has
required major alteration to the front of the crankcase to house the
starter motor. Some other modifications include the plugging of the
kick starter hole and the removal of the XT's decompressor
Performance of the bike feels
substantially better than it looks on paper. The SR will accelerate
quite rapidly and smoothly in almost any gear without fuss. Its
maximum torque comes in at between 6000 and 7000 rpm and it's a very
usable powerband for city work. Unfortunately, the open road does
test the limits of the SR. Its single cylinder's power does not
match that of twin cylinder 250's and therefore under hard work
conditions, the bike starts to show its limits. For example, we
found that two-up and into a strong headwind the SR was stretching
to hold 100 km/h on the flat in top gear. This failing could be put
down to two things, i.e. the low engine specific power output of
41.0 kW/litre and the high weight to power ratio to 21.5 kg/kW, both
of which give a 15% advantage to the CB250RS Honda.
One very impressive note though
is the excellent fuel consumption. Our test bike achieved a best
touring consumption of 29.2 km/I (82.4 mpg), slightly less than the
250RS Honda at 30.2 km/I. City riding returned 27.5 km/I (77 mpg),
substantially better than 24.3 km/I for the 250 Honda. Overall we
averaged 27.8 km/I (78.5 mpg) out of the SR250 which is very good
for the type of transport it provides.
On the strip and dyno
The dragstrip running and
dynotesting of the SR250 was plagued with many problems because of
the lack of a tachometer. We solved the dynotest problem first (an
explanation later) which in turn allowed us to cross reference the
bike's roadspeed with an actual engine speed in each gear. So we did
have, in a roundabout fashion, a tachometer for running the bike on
From the resulting figures, the SR250 was a consistent performance
machine. The best time of 17.2 seconds at a terminal speed of 119
km/h appeared quite frequently throughout the testing session.
The running of mid 16's put
forward in other road tests appears too fast considering the fact
that the similarly equipped and geared XT250 could only run 17.6
sees (TWO WHEELS June 1980).
Best performance was obtained using slight clutch slip at the start
just to keep the engine over the 6000 rpm mark. Gearchanges were
made at about 8500 rpm (according to the speedo) and the final run
to the finish line was in fifth gear at approximately 7700 rpm.
As mentioned previously, on the dyno we had to measure the engine
speed without a tacho. This did present some problems. An electric
tachometer had to be wired into the firing circuit and
cross-referenced with the true rear wheel speed.
This arrangement then allowed us
to match bike roadspeed with engine revs in each gear. The test
figures we achieved were as predicted, i.e. rather lower in all
cases than the four-valve RS250 Honda.
Maximum power of 9.8 kW is produced at 8000 rpm and torque peaks at
7000 rpm with a value of 12.3 Nm.
These figures are somewhat lower
than the RS250 Honda which returned 11.6 kW at 8500 rpm and 12.6 Nm
at 8000 rpm. The SR250 dyno curves are however very similar in shape
to those of the Honda, i.e. almost constant torque value from 3000
rpm to 8000 rpm and gradually increasing power curve. Most of the
engine action happens within the 7000 rpm to 9000 rpm region, a
power-band that needs to be utilised extensively on the open road.
In the city however, adequate performance can be achieved from the
SR by keeping the engine revving between about 3000 rpm and 7000
rpm. The single cylinder
Honda models. Actuation is by the trail-bike style rack and pinion
system which usually gives good feel and does give light lever
action. Throughout the test we encountered no problems with the SR's
clutch and found it adequately specified to take the load put
Gear ratios turned out to be well
chosen for road work considering they were originally designed for
trails. Our slightly higher self-imposed redline of 9000 rpm allowed
the SR to run to 43, 67, 90, 114 and 139 km/h in gears 1 through to
5. Top gear as mentioned previously did find the going a bit tough
under hard riding conditions and one could not expect to cruise
comfortably on the open road at more than about 120 km/h.
Gear-lever action was light and positive with no false neutrals
dispersed throughout the gears. Neutral itself was very easy to find
and maximum change points could be felt from the power drop-off of
the engine. Overall, a well proven setup taken directly from the
trail bike version.
Suspension, frame and handling
The general stance of the SR250H gives a good indication of what the
suspension will probably be like. For example, the long travel
(140mm) front forks do give a nice, well-sprung ride with adequate
extension to dampen nearly all suburban road bumps. Damping is well
catered for and the front wheel stays where it should under heavy
braking or cornering on uneven surfaces. Rear suspension is somewhat
more limited with only half the amount of travel of the front forks
The rear consists of KYB shocks
inclined moderately forward and surrounded by a variable rate
spring. Spring preload is adjustable over five settings and
generally the second lowest setting is adequate for one-up city
riding. Two-up (depending on the road) needs the highest setting to
retain the bike's original handling characteristics. With a
passenger present, the combined load might pass through a position
directly above the rear axle. This does not do anything for the
One up, the bike does handle well
around town, once one is accustomed to the light feel of the front
end. The riding style suits commuter riding ideally with almost
every rider being able to place his or her feet squarely on the
ground (every bike rider's dream). Medium and high speed cornering
is quite steady due mainly to the bike's low centre of gravity. The
bike can be thrown around with some confidence.
Design economies in the SR250H first creep up in the brakes. The
bike comes equipped with a single-leading-shoe drum brake at both
front and rear. The front brake is cable operated and the rear, rod
operated. Since 80% of the braking effort is taken by the front
brake, we were somewhat worried by the half-width drum rather than
the more usual single disc setup. In fact if it wasn't for the size
of the front wheel, one would suspect that this was lifted straight
off the XT.
These fears were not particularly
justified. In the 60 km/h to zero stops, the SR fared very well when
compared to similar but better equipped machines. Our best stop of
12.1 metres was very close to that obtained by the Honda 250RS with
its front disc setup. Over the higher speed stops, the limitations
of a half width single-leading-shoe brake did become obvious. Quite
dramatic drop-off of braking power was felt even during the first
hard stop from 100 km/h. The cable operated front brake, although
providing good feel and easy leverage, had to be adjusted up mighty
high to stop the brake lever from being pulled onto the handlebars.
Front brake lockup was not the easiest thing to do but the rear
wheel could be stopped fairly easily. The extra distance caused by
the brake fade is notable, i.e. 37.3 metres for the SR250H versus
34.4 metres for the CB250RS.
Wet weather braking is not too bad providing the drums don't get
soaked, and if that happens — forget about stopping at all.
Throughout the braking session the SR didn't give any dramatic
breakaway performances and from that we concluded the bike was
pretty stable under heavy braking conditions.
Bits and pieces
The most striking aspect of the
SR250H is the quite obvious low budget look about it. Lets face it,
to knock out a 250 single for around $1300, one has to really get
serious about savings. For that reason, the SR250 does have a
spartan appearance — just a straight single colour (non metallic)
paint job with a Yamaha badge on each side of the tank and a 250
decal on the side covers. Wire wheels complement the look.
The most notable omission is the
tachometer. There are no super-looking square indicators (although
those fitted do bend), and beautiful pinstripes along the tank are
definitely out this year.
What the SR hasn't got doesn't in any way prevent the bike from
doing what it was designed to do, i.e. provide economical transport
for the novice or experienced rider.
On the positive side,
engine appearance is very good, the alloy work and finning are of
high quality as always. Chromework on the exhaust pipe is very good
and overall the appearance of the powerplant is appealing.
We liked the inclusion of electric starting, the electronic ignition
and the larger more economical carby — obviously Yamaha had their
priorities right when they started to save dollars.
Riding position, as mentioned
previously, is good but long-legged people could find the leg angle
too acute when feet are on the pegs. The large, wide and high
handlebars give very good steering leverage. Thankfully they aren't
rubber mounted like those on the 650SF Yamaha. One grievance with
the bars is that once in the riding position, one's elbows just hang
there and get tired. The forearms are neither straight nor are they
supporting any of the rider's body weight, as they would be under
normal conditions. Out on the open road the situation gets worse and
after about an hour's riding the rider's forearms are usually very
tired. A nice set of flat bars would most likely solve the problem.
The seat is also too short and fat to
provide comfortable accommodation for passengers. Most pillion
passengers end up sitting on the grab rail behind the seat wearing
their knees around their chest because of the high footpegs.
Instrumentation well what can you say? A zero to 140 km/h
speedo is all you get — no trip meter, no tacho, in fact the speedo
looks like the type they used to use on those early Honda step-throughs.
Controls are well placed and include auto-cancel indicators, kill
switch, headlight flasher, electric starter and steering lock
integrated with the ignition switch below the speedo.
Other notable features are the bend-able indicators, trinkets box
(which I always thought was a fuse box) found between the handlebar
mounts and a sight glass for engine oil.
The styling exercise of Yamaha's SR series has proven popular with
the 650, 750 and 1100 models, so there seems no reason why the SR250
should not find the same acceptance. Of course its acceptance is
limited by the laid-back appearance which would obviously not appeal
to everyone. Possibly the sheer practicality of design, ease of
operation and economy is really what will grab the buyer, because in
that area the SR is tops. Almost anyone from learner upwards can hop
on the bike and feel at ease with it. The low seat, easy to reach
bars and smooth torquey delivery of power from the 250 single engine
all combine to make riding the fun it used to be. We feel quite
positive that at the price (about $300 less than the 250RS Honda),
the SR250 has got to be a winner.
Source Witch Bike 1980