Report From Japan
REPORT FROM JAPAN
JACK YAMAGUCHI
HONDA CHARIOT
Honda built a couple of ST70 (affectionately called "Dax" in Japan) sidecar outfits to transport the most meritorious players in our pro baseball series in a parade marking the finale of the season. The sidecar is not what we normally call a "chair," but is merely a platform with a tall shield (armor plate to fend off rotten apples thrown by enemies). The present configuration is definitely tail heavy, and tends to lift the front wheel, unsettling the poor passenger. Driving his mini outfit is great fun, and I gather Honda-san is seriously considering producing a more habitable mini-sidecar for the ST70.
RACING YAMAHA STYLE
A recent clubmans-type road race meeting at Suzuka demonstrated that Yamaha meant business in this type of innocent, fun-for-all racing. Races sanctioned by the Motorcycle Federation of Japan allow only production motorcycles, and bar such professional machinery as Yamaha’s dreaded TD and TR models. So Yamaha entered highly modified X series Twins in two senior classes through an ex-factory-rider-turnedtuner, one T. Noguchi, who was said to enjoy full support from the Hamamatsu quarters and who had direct access to the factory parts bins.
A new AX125 Twin ran away from the rest of the field in the senior 125cc class, and a couple of RX350s and a DX250 flew in a perfect formation in the 250-and-up class to finish 1-2-3. The winner, A. Motohashi on an RX350, was timed doing a 2 min., 30.9 sec. lap, which was within 2 sec. of the all-time record established by no less a talent than Mike “the Bike” Hailwood on a Grand Prix Honda 250 Six on this track. I almost felt sorry for genuine clubmantype racers who worked so hard on their 750 Fours and 350 Twins.
Apparently Honda and Kawasaki tuners weren’t quite ready with their promising CB500 Fours and 350SS Threes. We hope to see a recurrence of the Honda-Kawasaki duel, which has taken place between the CB7SO and Mach Ill brigades for some time. Suzuki must also be busy preparing machines for the motocross championship series, both in Japan and abroad, because they are doing very little as far as road racing goes. Kawasaki prefers to encourage private riders, much the same policy as its U.S. subsidiary. Its modified GAIl Single is one of the most popular racing bikes favored by young, upcoming rid ers. This potent 90cc bike may be bought for something like $550, ready to race. Of 41 starters in the Novice 90-cc event in the Suzuka race, 30 were astride Kawasakis.
HONDA CB 350, 250 AND 125
Leading maker Honda has further consolidated its mainstay CB series by introducing new versions of the CB350, 250 and the 125. As for the mediumweight CB 350 and 250 models, the most noteworthy technical refinement is their front disc brake, which was first incorporated in the 750 Four. The disc brake-fitted CB350 and 250 are designated senior type. Like their bigger brothers, the 750 and 500 models, they feature an ignition kill switch on the right, and a speed warning lamp which works at over 50 mph for the improvement of safety. They are also fitted with a new helmet holder like that of the CB500 and 50. Other technical data are the same as their predecessors.
The new version of the CB125 features a striking new fuel tank. Other modifications are a separate tachometer, a helmet holder and an improved air cleaner and muffler to hold engine noise to a minimum. A tuck-roll type seat is also a new touch to the CB 1 25 line.
YAMAHA TRAIL RT 360 AND DT 250
Yamaha is claimed to be a trail age trendsetter with its sophisticated line of trail models which meet the needs of customers over the widest range.
Recently the company unveiled new versions of its bigger trail models, the RT 360 and DT 250. The models look like their predecessors in appearance; both, however, feature striking technological refinements. Most notable are a seven port cylinder barrel and reed valve induction.
A single-cylinder, two-stroke engine equipped with piston reed valves has a revolutionary function, in that the intake port acts as an additional scavenging port, too. In other words, one more booster has been added to the convenlional two main and two sub-scavenging ports, thus increasing scavenging efficiency for the improvement of torque.
In the intake/scavenging phase, with the piston moving upward, negative pressure in the crankcase becomes higher. The moment the inlet window on a piston reaches the intake port, reed valves open to induce mixed gas. In a word, this new' system starts mixed gas inducement faster than a conventional piston port engine.
As the piston moves further upward, the intake port fully opens to induce a large quantity of mixed gas through reed valves. 'Then, exhaust and scavenging ports close to be ready for the compression stroke.
Mixed gas which has been compressed into a combustion chamber on the upper part of the piston ignites and explodes. Then, the piston moves down ward. Naturally, a new intake of mixed gas in the crankcase is compressed by the lower part of the piston to close reed valves, thus preventing any blowback.
The piston moves further downward, and the exhaust port opens to discharge gas rapidly. On the other hand, mixed gas is further compressed in the crankcase. The gas is partly compressed into a reed valve chamber through the piston’s inlet window.
The piston keeps moving downward. Two main and two sub-scavenging ports open, and a new intake of mixed gas which has been compressed in the crankcase begins to flow into the cylinder, thus driving out used gas through the exhaust port.
This function is called a five-port scavenging system. Yamaha’s new system, however, adds one more port to increase scavenging efficiency to a maximum as follows: The upper part of the intake port opens to induce mixed gas into a cylinder through the reed valves. Then, the inertia of gas flow together with the pulsatory motion of the fiveport scavenging function opens the reed valves for the sake of an entirely new scavenging function. In a word, the intake port serves as an additional scavenging port, and the merits of this unique direct scavenging system are self-evident in producing more torque at all engine speeds.
