BULTACO TSS ROADRACERS

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1-2-3 Bultacc .ctory In tl 2 5 0 ~ ~simple, piston port, two-stroke single could pull off
a G P win?
class of the 1966 Ulster Grant- - rix will go --wn in
This story is even more fantastic when one considers
motorcycle racing history as one of the most decisive wins
that there is no such thing as a "works" Bultaco. There
by a small factory. Even more startling than the 250 vicare a few riders who are "helped" by the factory; these
tory, was Tommy Robb's ride to third place in the 350
include Ulster winner, New Zealander Ginger Malloy,
race, behind Hailwood and Agostini. Riding a 251cc
Ireland's Tommy Robb and even our own Jess Thomas,
Bultaco and giving awi almost '^?ccs, he beat some
when he did his stint in Europe. This help is usually a
and i sf the British profull-sized factory machi
pair of loaned machines and a few parts, but the machines
duction racers.
are the same as any private owner may buy for himself.
True, the might- '-anese f - -'~ries were not on
Ulster winner Malloy was forced to pass up the Isle
ley we1 nere. And it will be
hand in full strength,
of Man races two weeks later because the T T does not
some time before people forget the David and Goliath
pay sufficient start money to make it worthwhile for a
battle that took place on the wet roads of Dundrod, for,
private owner. Although it may seem unjust in some rein this day of rotary valves, four and six-cylinders and
spects, Sr. Bulto prefers to help many riders with his
the like, who would suspect that an almost embarrassingly
HE OUTSTANDING
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BULTACO TSS ROADRACERS
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CYCLE WORLD
Occasionally, though, Bultaco has made large changes
of a major redesign nature; for instance, there was the
change to six-speed transmissions which permitted a rider
to have a gear for any situation. Then, too, a big step
was taken when the factory went to a full-sized 250,
thereby discontinuing the 196cc TSS, which had been
competitive in 250 racing, although it was giving away
a 50cc displacement advantage. Next was probably the
biggest step of all, that of changing to water-cooling for
the cylinder head and barrel. Not only were these major
engine components changed, but the frame main cradle
has been altered to accommodate a radiator.
There is little doubt that water-cooling offers advantages. If a two-stroke single is tuned to an extremely
high degree, there will be very high internal temperatures,
particularly in the region of the exhaust port, and the
possibility of a piston seizure becomes more likely. The
biggest danger of all occurs when an engine is properly
tuned for the prevailing conditions and a climatic change
takes place that causes the internal operating temperatures
to be higher. This can happen through less efficient
cylinder cooling or by throwing the carburetion off,
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liereby causing a lean mixture and the resulting higher
cylinder temperatures. When the condition is borderline,
the rider may not have any indication that something is
.,amiss; there may be no pinging or erceptible loss of
'power. ,However, as soon as he rol s off the throttle
'slightly, or begins to climb a hill, or enters a bumpy
, section of a course where engine revs are apt to fluctuate
greatly, there is the danger of sudden temperature rises
that can lead to piston seizure and subsequent disaster.
Water-cooling offers a safety margin in that the cooling medium and jacketed engine components are less
affected by atmospheric changes; outside temperature
could change by a wider margin without an upset in carburetion or a marked change in operating temperature.
.-The benefits are two-fold: the tuner can jet closer to
maximum power output and the rider need not fear the
dreaded locked-up engine.
The Bultaco cooling system does not employ a water
pump to circulate the coolant. Instead, it relies on the
"thermo-syphon" principle, which has been in use on
water-cooled racing two-stroke motorcycle engines for
more than half a century. There is nothing mystic about
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thermo-syphon; if water is heated, it will rise. In the case ;of the Bultaco system, the water rises through the cylinder head into a hose connected to the to^ of the radiator.
and cooler water is pulled from the bottok of the radiato;
to replace the water that has moved out of the jacket.
Should there be a sharp temperature rise anywhere in the
jacket, the water will be heated more rapidly and therefore move upward faster, resulting in cooler water moving
into that area at a higher rate. Thus, quite effective cooling is obtained.
One disadvantage with thermo-syphon is that a time
lag exists between a sudden temperature rise and the
movement of cooler water at that point. Bultaco has been
able to overcome this problem somewhat by operating
the system at 8S°C.,which ensures quite good movement in the system at all times. In order that the rider
may know what is going on, an easily read, rubbermounted temperature gauge is mounted just below the
gas tank, inside the fairing on the right, with correct
operating temperature corresponding to 12 o'clock. The
engine should never be run hard until the temperature is
at least 70°C.
Engine-wise, the Bultacos are probably the simplest
m'achines in international racing at the present time.
Femsa electronic ignition eliminates the need for contact
breakers or any parts actually contacting each other.
Some riders in Europe have completed a whole racing
season without the timing requiring any maintenance
whatever. However, when one has a plus, there is also
a minus, and we found the Bultacos frequently need a
very brisk push to light them off.
We do not completely believe the horsepower figures for these engines. The engines are certainly strong,
particularly the 250. The 125 is giving away some horsepower by using a constant mesh gearbox, where all of the
gears are revolving, rather than only the gears in use/
Bultaco now employs two Dykes pattern piston rings in
place of the one ring on previous TSS engines.
Externally, the 125 and 250 TSS Bultacos are identical, except that the 125 continues to use the auxiliary oil
feed into the carburetor bell from a small tank under
the seat, while the 250 relies strictly on the oil/fuel mix.
The frame and motorcycle parts are the same on both
machines; an ideal situation for a private owner, because
he has a higher degree of interchangeability. But, it is
also the major downfall of the 250. The brakes, which are
just passable on the 125, are not up to the task for the
larger machine, especially if the rider starts to "get on it"
on a twisty circuit. What is really strange about the similarity in machines is that, although one has double the
displacement, both use the same size carburetor! The onetwo-five does not display any of the symptoms usually
connected with an engine that is over-carbureted, as it
runs clean through the whole range. The two-fifty is probably the most tractable racing single we have ever ridden,
and is on power all of the time. This would seem to
indicate that a larger carburetor could be used, because
the close ratios afforded by the six-speed transmission
permit a fairly narrow power band.
Except for the previously mentioned frame alterations
to accept a radiator, the frame confi uration is basically
the proven Bultaco layout. A large- ameter top tube is
generously gussetted to two front down tubes which, in
duplex fashion, continue, without joints, upward to form
the rear frame and carry the tops of the rear suspension
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units. From these rear frame tubes various pieces of
tubing are nicely triangulated to the main cradle member
running vertically down to the engine/transmission unit.
The swing arm is mounted inside the frame side members and features unusually large gussets. Like all good
production racers, the Bultacos seem to fit almost anyone
who climbs aboard. Seat-to-handlebars and seat-to-peg
distances are ideally suited to an average size rider, but
even a six-footer can tuck in without too much discomfort.
Bultaco has used the samk front fork design on
all of the TSS racers and well they should, as the forks
are excellent for road racing.
It is very likely that the more experienced a rider is
at roadracing, the more he will appreciate the Bultacos.
The 125 is easier to ride, probably because it has the
same chassis and running gear as the 250 and, therefore,
a poorer power-to-weight ratio which makes it more
tractable. Whatever the reasons, the 125 is still very
quick and can be. ridden with more precision and rider
confidence than any production racer we have had the
opportunity to ride.
Although handling on the 250 is excellent, it does
require considerably more discretion than the smaller
one. On fast, bumpy curves it will shake the front end
a bit, but this feels more like a function of power, speed
and light weight, rather than the unpredictable yawing
usually associated with bad frame design. Now, after
having had the chance to ride the 250, we can better
understand how Tommy Robb managed to beat those
350s at the Ulster GP. Unfortunately, we will not see
these machines competing in AMA racing; one of the
archaic rules still in existence bars water-cooled engines.
We can, however, look forward to seeing them in
AAMRR, AFM and ACA races.
Because standing-start 1/4-mile acceleration has little
meaning as a guideline for evaluating the worth of a road
racer, we dispensed with this phase of testing for the
Bultaco TSS machines. However, to satisfy our curiosity
- and just for chuckles - we fitted the 125 with a
a 50-tooth wheel
14-tooth countershaft sprocket'and
sprocket (8.5 : 1 overall top ratio) for a few runs through
the lights. Speed was an outstanding 84.5 mph, compleH
mented by a time of 17.6 seconds.
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