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►Charles Darwin's island
animals could not have followed a more clearly defined course of evolution than
have the 350 Yamahas. A line of fairly well adapted and very well established
250s have watched new generations of bigger brothers first mutate ever so
slightly into 305s and then to full 350s.
From the primordial soup of German Adlers, whence came the
first Yamaha twins, it was almost impossible to distinguish between racing and
touring as parent/child. In 1967 Trevor Deeley, then the Canadian Yamaha
Importer, brought to the Indy National a 350 road racer that had been converted
from a 250 in his shop. Before the bike expired with a terminal case of teething
bothers, then little-known Yvon duHamel had unceremoniously raced it through the
pack and momentarily passed the race-winner, Cal Ray; born, on his 750 Harley. A
lot of people either didn't see that historic event or refused to believe their
eyes. The unbelieving were given another demonstration at the following Spring's
Daytona: Mike Duff qualified a 350 second-fastest at over 147 mph, and two other
Yamahas finished the race in second and third places behind Rayborn's big H-D.
So it has been ever since: Yamaha 350 racers have been beating bikes with
engines twice as big and the street counterparts have gotten better and faster
just as steadily.
A first,
even casual ride immediately drives home the essential nature of an RD 350B. It
is stiff and taut and at times has a shade of race-bike reluctance. The first
display of this reluctance is met in the engine's starting. Or perhaps it simply
is more lethargic than reluctant. Two-strokes get twitchy during starting when
the carburetor mixture is not rich enough or if there is not enough of it.
Mikuni blessed the world of the two-stroke with a completely separate metering
system for cold-engine starts. Most Japanese bikes have one of these cold-start
systems in each carb. But Yamaha embraced economy and simplicity by using a
cold-start device only in the left carb and connecting it to the right carb with
a length of hose.
When the
starting device is actuated by a thumb lever on the left carb, the Yamaha is
ready to start after the ignition switch (conveniently located between the
instruments at the handlebars) is on and the fuel valve handle is vertical.
Normally a Mikuni-equipped two-stroke will fire immediately if the throttle is
left completely closed. But the siamesed system does not provide enough mixture
to easily rouse both cylinders. This causes the rider to have to alternate
between closed and barely-opened throttle until the engine catches and clears.
On a brisk morning, we found that the best procedure was to push the kickstart
pedal through four times to prime the shared system and then crack the throttle
slightly when the engine sounded ready. The number of engine revolutions per
kickstart stroke is relatively high, so the pedal resistance is considerable.
But not so great one has to leap up in the air before each try, as with a big
four stroke.
Once the
engine cold-naturedly coughs to life, it remains balky but does not attempt to
die unless the enriching lever is prematurely closed. Pre-dawn staggers fade
quickly with the light of engine heat, however, and exhaust sound steadies into
a romping, insistant, bramp-bramp-bramp that is strongly reminiscent of the
first 500 Kawasaki triples. One can't simply motor away smoothly on an RD 350B:
the revs must be held at about 3000 while the clutch is gradually engaged to
couple the transmission and engine. At about 4000 rpm the engine begins to
cackle along happily at constant throttle. Twisting the throttle open in low
gear produces a gradual, easily controllable wheelie. A full-power shift to
second brings the wheel back up about a foot. Through third and into forth gets
you to 60 mph in less than five seconds and the scenery is beginning to blur at
the edges. In just over 14 seconds, the bike is approaching its rpm red line and
is hurtling along at over 90 mph. The tach needle easily touches 8000 rpm in
high gear (sixth!) and you back off the throttle to keep the engine from
fragging itself.
So little
noise and vibration accompany such a spurt that the rider must -rely on his feel
of accelerative force and visual judgment to perceive how quickly he has
attained a high rate of speed. It is extremely unusual for a high-performance
bike to be so smooth and quiet. The lack of commotion makes the speedometer and
tach readings difficult to believe.
Blasting
along twisty, deserted roads proves the RD 350B's suspension to be almost as
good as the engine and gearbox. Both the forks and rear shocks have high damping
rates to control the rebound movement of their springs. The front springs are
stiff, and keep the front of the bike from diving far enough to cause sudden
clearance problems when the throttle is closed approaching a downhill curve.
Three possible preload settings are provided on the rear shock springs and the
stiffest setting was required to match the fixed fork preload for our 160 pound
rider. Thus adjusted, the machine will not oscillate in high-speed sweeping
turns.
Ground
clearance is limited by the steel footrest mounting bars. These bars hit just
after the ends of the rubber footrest rubbers drag on flat turns, but give no
warning before sending the sparks flying on hog-back curves. Fairly hard riding
is required to find the clearance limits.
The standard
Japanese Dunlop tires are much better than the rubber that usually comes on 350
street bikes. A ribbed-pattern front (3.00-S18) gives extremely sensitive
steering response with almost neutral feel through the handlebars. Dunlop's
designation for this tire is F7. The rear tire has a universal pattern, is
designated K95, and the size is listed as 3.50-S18. We have as yet to hear an
official explanation for the new S sizing designation, but the tires seem to
have a wider tread profile for a given cross-sectional carcass size as compared
to conventionally proportioned tires. The K95 rear gives first-rate directional
stability and allows plenty of cornering traction within the bounds of the
clearance dictated by the footrest bars. When traction does get scarce, the tire
begins to feel crawly and the rear end of the bike slides predictably.
During fast
road riding and our instrumented braking tests at the drag strip the brakes
performed completely without fault. The rear has a good, strong, progressive
feel and the front disc is absolutely incredible. Until we got this year's RD
350, the quickest stopping bike we had ever instrumented was last year's RD 350
in a stop that corresponded to an average g-force of .998. Thanks to the nice
wide footprint laid down by the front tire, and the tire's unwillingness to
distort laterally, this year's model established a new record by decelerating at
an average rate of 1.04 g from a true 60 mph to a complete stop. A good hard
squeeze is required to keep the front tire on the verge of locking, but you
don't have to pull so hard that no sensitivity remains to monitor the possible
consequences. Nothing unusual about the brakes was noted during the test other
than their ability to stop the Yamaha in the shortest 60-0 mph distance we've
ever recorded.
The
combination wrought of the stiff suspension, good street tires, and fairly
neutral steering geometry of 27.5 degrees rake, 4.17 inches trail, and a rather
short 52-inch wheelbase gives the RD 350B a very precise but quickish feel that
is underlined at all times with unshakeable stability. The rider can feel every
pebble and seam in the road but quickly learns to ignore them. This stability
and sure-footedness combine with perfect body-to-bike fit to leave one's senses
free to experience the rush of wind and road.
When the
six-speed gearbox was introduced in the Yamaha 250s and 350s three years ago,
many of us figured it was merely a ploy to legitimize the arrangement for the
purpose of AMA-ruled racing. And such may have been the case, for many countries
still get five-speeders as the standard retail fare. But ploy or not, the
six-speed gearset gives an RD 350B the extra dash of the spice of performance
that transforms it from a mere sporting middleweight into a genuine
middle-weight Superbike. An examination of the performance chart will show that
the standard gearing is set for the engine to just peak in high gear at the end
of a quarter-mile. The six speeds allow the engine to keep within its most
efficient rpm range from a tire-smoking start to the peak in high. The result
was best quarter-mile run of 14.12 seconds at 93.21 mph. Those figures utterly
overshadow any generated by the Yamaha's immediate price/engine-size competition
and put the RD 350B on performance-par with many 650s and 750s.
Back out on
the country roads, the right gear is always available to prevent any instances
of the dread Lazy Tach Needle. Any time the rider gives the grip a twist with
the tach reading between 5500 and 7000, a really gratifying surge of
acceleration is right there, ready and waiting.
Several
aspects of the RD 350B's character make it rather compromised as a general
transport mount. The stiff forks and shocks, which gave good cornering control
at high speeds, also provided our 160 pound rider with punishing jounces from
freeway seams. A 200 pounder found the bike too soft on the country backroads
and about right on the freeway. Our 130-pound art director developed
eyeball-rattle and split vision either place, because for him the springs
wouldn't yield at all. True progressive-rate springs in the forks and shocks
would be the answer, but the cost and manufacturing difficulty involved in
making the springs will keep them from being standard equipment. The big and
little RD 350B owners will be obliged to hunt out fork and shock springs to suit
their own needs.
The engine
also contributes a bit toward everyday touring bothers. A combination of the
highly-tuned cylinder breathing and a pair of genuine low-quality ignition coils
give the bike a high rpm misfire that is a cause of some concern when there is a
loaded gravel truck to overtake in the only passing zone for 20 miles. Yamaha's
specified spark plug for the RD 350B is an NGK B8HS, which is supposed to have a
very wide heat range electrode. If the plugs are new, they function okay for a
while. But after a day's normal cruising, enough deposits built up on the plugs
to cause the had misfire when the rider downshifts to make a full-throttle pass.
We fiddled around with the engine for a couple of days trying to trace the
malady to its source. A look at the ignition coil output trace with an
ocilloscope showed that the output voltage of the coils is about 40 percent
below what is delivered by a normal automotive coil. Our scope is not designed
to give kilovolt readings in numbers, but it does a good job of comparing coils.
In such a situation there are a couple of immediate solutions: increase the
spark voltage by changing the coils, or decrease the spark plug resistance. The
plugs were not excessively oily or fuel-fouled so it wasn't simply a case of
installing a hotter heat range. Several of the spark plug manufacturers make a
special group of plugs for two-strokes which have fine-wire center electrodes
composed of an alloy (gold, palladium, etc.) which will cause a spark to jump a
given distance at a considerably lower voltage than conventional plugs.► |
