1972 Yamaha XS2

1972 Yamaha XS2

The Yamaha XS2 released in 1972 sported the first disc brake and electric start in the model series. The electric start was a quirky system that used a decompression lever that lifted the left exhaust valve during the starting process. There were few changes cosmetically with the main ones being changes in paint colours and removal of the front fork gaiters. Unfortunately, Yamaha made no changes to improve the handling in this model.

Yamaha XS2 Brochure

Road Test from Cycle News 1973

YAMAHA 650: A Different Ocean but the Same Idea

The Yamaha XS2 is an abnormal extension of Japanese technology. The extension, which was attempted by Kawasaki a few years back with limited success, is not one that would seem to be fitting 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 with at age three instead of twenty but, in many respects, is far more of what twins are 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 XS2, more than anything else, is an extension of the 350 Honda. It is a clever move by Yamaha to build a bike that is aimed at the majority of the motorcycling public. in the large displacement class they have left themselves open to profits by creating a bike for which they can charge 50% more than a 350 Honda. The tooling costs are not 50% greater for a 650 than a 350, and the profit margin gets larger. The XS2 will make bucks.

The XS2 is easy to find fault with. No one was very excited about testing it when it arrived. Everyone figured, “Yuck, a Limey bike without personality.” On the contrary, that’s what the XS2 is about. It has personality. It’s mellow. It took British manufacturers decades to get where the Yamaha 650 has gotten in three years, if they have gotten that far.

Yhe Yamaha 650 took 500 miloes to settle into any kind of pace. Break in was slow and not necessarily pleasant. But by the time the odometer ticked around 500 things had begun to settle. Vibration, which had at first been quite prominent, began to become subdued. The engine began to idle consistently. Throttle response improved, and acceleration increased considerably. Getting through the 500 miles wasn’t pleasant, and it was difficult to resist reaching a conclusion on the basis of the break in period. But it did get better and continued getting better throughout the test. With nearly 600 miles on the engine, it finally began to think about doing something above 6,000 RPM other than rattle one’s fillings.

Mellow at Age Three

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 a motorscycle 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 and things that detract, but will never provide the intimate feeling of the whole experience. However, maybe it will do to let you know what the pieces do and don’t do. 

The motor is an overhead camshaft vertical twin, with a bore and stroke of 75×74, resulting in 653cc. The engine does not have Yamaha’s new gimmick, the Omni-Phase Nalance (trademark). Oil for lubrication is carried wet sump style below the engine and none of it ever found its way out through the 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 difficulty of access to the intake valve adjustment.

Feeding each cylinder is a Mikuni 30mm constant velocity type carburettor.  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 5,500RPM. These were the only major bugaboos of the powerplant and seemed to prohibit the twin from working the way it could have. One choke lever on the left carburettor assisted starting and provided enrichment for both cylinders through a venturi 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 ZS2 will kick back, catching the wary off guard.

All of the not-particularly awesome power, but considerable torque, is deliverd unto the rear wheel through a five speed transmission and a wet multi-plate 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 because it allows one to accelerate through the gears in a constant 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 6,500RPM. The only problem encountered with the transmission was an unwillingness to shift down more than once without 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 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 70MPH (4,300RPM) brought about 40MPG and with the 3.9 gallon tank, it was conceivable to stay in the saddle for about 140 miles. No one 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 changeover to decent accessory shocks would also take care of high speed oscillation problems, I am convinced.

The electrical system components functioned with typical Japanese efficiency, producing lots of light dependably. On the left handlebar was a switch box containing headlight on/off, dim switch, and turn indicators, Once during the test, in a moment of haste, my trusty left thumb mistook the on/off switch for the dim switch. Fortunately the consequences weren’t dire. Since the right handlebar has only the kill switch in the switch box, it might have been neat to put the on/off 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 brake light. That has to be changed.

Some acquaintances who do custom painting on bikes  were hot to do a number on the XS2.

“Let’s see, throw away the plastic side covers with the chrome uglies, a nice midnight blue.”
“Uh huh, get rid of the frilly stripes on the tank”
“Sure is a nice looking engine”
“Wretched welds”
“The turn signals are ugly, but I bet they work well and don’t blind you” 

So as you can see, the XS2 is a natural for custom work. Look around you, lots of people think so.

Handling of the bike hinged around one thing, the tyres. Tyres supplied are a Dunlop rib up front and a K70 on the rear. Both are of Japanese issue and neither work very well. They made what seemed to be a basically nice handling bike scary. Riding was a constant guessing game over break-away. Unless ridden very, very smoothly or with a passenger, break-away always occurred before anything would ground. They didn’t give an impressive amount of warning but would give a second chance.

A most disturbing sensation occurred when cornering hard in first gear. If done carefully the bike could be leaned until the footrest touched but adhesion was borderline and getting the gas back on was really touchy. Because the 650 has no rubber dampers in the rear hub (or clutch) there was a slight snap when rolling the throttle back on. This was enough to cause the rear end to “walk out” a foot or so. Scary.

The rib up front did cause the bike to point well. It went just where you wanted it to go. It ran amok in freeway grooves slightly but the friction steering damper took care of most of it. That damper, incidentally, was mandatory for any aggressive riding as the bike seemed to be too quick without it. Ridden a hair bleow “fast” the XS2 was confidence inspiring and responsive. it did just what it was told and if you didn’t tell it, it would usually do the right thing in spite of you.

If and when you got in over your head the brakes could save the day. The disc brake on the XS2 was the best brake I’ve ever used. It was powerful and sensitive and seemed to be reasonably light weight.

Those are the component pieces of the XS2 which don’t add up to the whole. Listing them has caused me to question slightly why I liked it. But when I ride home tonight I’ll remember. I’ll be riding on a bike that vibrates some, makes a little too much noise (but nice noise), isn’t too comfortable to sit on, and the guy on the 750 seven cylinder and blow me off. But none of those things will bother me much.

You see, I finally learned what big twin cylinder motorcycles are about and Yamaha helped me do it. Unlike it’s competition, it doesn’t leak; it vibrates less; it is more comfortable; it stops better; when all components are considered, is is no doubt more reliable; and it costs less.

Those are hard to affront reasons for buying a 650 Yamaha instead of its competition. As far as wanting a large displacement vertical twin, don’t knock it until you’ve tried one. If you don’t like it you can always call it the “Excess Too”.