Cycle News - Archive Issues - 1970's

'" i e, M ,... '" (D' .ri " LL ~ w Z W ..J U >- U YAMAHA 650: A Different Ocean but the Same Idea by Dave Schoonmaker The Yamaha XS-2 is an abnormal ex tensio n o f Japanese tech n ology . The ex ten sion, which was attempted b y Kawasaki a few years back with limited success, is not one that would seem to be fitting to this age of multi-cylindered bikes. Yamaha has attempted it and by the number of 650 Yamahas rumbling around the streets of America, it's obvious that their move is a success. What the engineers at Yamaha have done is created a facsimile of a British twin that not only turned mellow at age three instead of twenty but, in many. respects, is more of what twins arc: supposed to be than its forerunners. Attempting to explain what a vertical twin is all about is a difficult thing to do, yet huge numbers of Yamaha 650, Triumph 650, BSA 650, Norton 750, Honda 450 and even 350 owners do know. All of these bikes are balanced motorcycles; moderation in all things. Only one, the Norton 750, rates as a superbike and still that's not what the Norton is really about. The XS-2, more than anything else, is an extension of subdued. The engine began to idle consistently . Throttle response improved, and acceleration increased considerably . Getting through the 500 miles wasn't particularly pleasant, and it reaching was difficult to resist conclusions on the basis of the break in period. But it did get better and con tin ued getting better throughout the test. With nearly 600 miles on the engine, it finally began to think about doing something above 6000 RPM other and things that detract. but will never provide the intimate feeling of the whole experience. However, maybe it will let you know what the pieces do and don't do. The motor is an overhead camshaft vertical twin, with a borejstroke ratio of 75x74, resulting in 653cc. The engine does not have Yamaha's new gimmick, the Omni-Phase Balancer (trademark). Oil for lubrication is carried wet sump style below the engine and none of it Mellow at Age Three? than rattle one's fillings. Magically, the 650 began to become fun to ride. As both bike and rider became broken in, riding started to become fluid. Pulling away from stop , lights produced a gentle but constant tug through the gears. Mountain roads rolled smoothly away with no impression of speed. All the things that the motorcycle could do came together into a flowing, soft and sensual journey. Itemizing the bike's capabilities will elucidate things which make it what it is ever found its way out through gaskets or exhaust pipes. 800 miles of testing brought no reduction in oil level. The only criticism about general serviceability of the engine concerns the difficul ty in access to the in take valve . adjustment. Feeding each cylinder )s a Mikuni 30Irim constant velocity . type carburetor. These seemed to work exceedingly well except when they didn't. When they didn't they responded fuzzily and actually caused the engine to falter under acceleration, at about 5,500 RPM. These were the major bugaboos of the powerplant and seemed to prohibit the twin from working the way it could have. One choke lever on the left carburetor assisted starting and provided enrichment for both cylinders through a ven turi balance tube. Starting was easy, once you learned the trick. When cold it liked the little lever on the right handlebar pulled in all the way, then slowly backed out. When hot just a touch would do. (That little lever .is a combination compression release and electric starter engager.) Kick starting worked fine but for the fact that the XS -2 will kick back, catching the unwary off guard. All the not-particularly-awesome power, but con sid erab le torque, is delivered unto the rear wheel through a five-speed transmission and a wet 'm ulti-p la te clutch . Overall gearing is tall, but the torque put out by the twin makes getaways painless. There is a fair gap between first and second, then the other three speeds follow closely. The closeness of the ratios is nice be cause it allows one to accelerate through the gears in a c o n stan t surge, but to a racer it probably makes little difference. The engine just plain doesn't care as long as it's between 2,500 and 6,500 RPM . The only problem encountered with the transmission was an unwillingness to shift down more than once without the reengagement of the clutch. Vibration produced by the motor was subdued and kind of pulsed away, doing little more than remind you that you were moving. At idle the whole bike shook in the, "Boy I got a wild , cam," style. Over a long distance the vibration might become a little fatiguing. But contributing much more quickly to fatigue are the bars, firm seat and stiff rear suspension. The bars promote curvature of the spine, which is torture after one hundred ' miles. Combine your bent back with shocks that are translating too much bump for the handling they deliver and you have a pain in your back. Cruising at 70 MPH (4,300 RPM) brought about 40 MPG and with the 3.9 gallon tank, it was conceivable to stay in the saddle for about 140 miles. Noone we found could do it, though. If I bought the bike (not unlikely) I would change the bars and the shocks, and the combination, I believe, would compensate for the firm seat. The c h an geo ver to de cent accessory shocks would also take care of high speed oscillation problems, I am convinced. The electrical components functioned with typical Japanese efficiency, producing lots of light dependably. On the left handlebar was a switch box containing headlight onloff, dim SWitch, and turn indicators. Once during the test, in a moment of haste, my trusty left thumb mistook the onloff switch for the dim switch. Fortunately the consequences weren't dire. Since the right handlebar has only the kill switch in the swi tch box, it might have been neat to put the onloff switch there. Instrument lighting was good and the instruments themselves were easy to read. There was one serious deficiency electrically. The brake light switches were not nearly sensitive enough. It took a near panic stop situation to bring any rise from the

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