The Motorbike Archives

Well, sir, for months afterward we have received scores of letters from Yamaha owners telling us we didn't know what we were talking about. Somebody at the factory must have been listening to what we were saying, though, because the new 750 vertical twin is as radical a departure from the earlier XS-1 and XS-2 as is conceivable. The factory has attacked a number of these problem areas and successfully solved the problems we found in the older 650 models.

Starting at the front of the machine the first thing you'll notice is the new disc brake, and it's a super stopper. It's very powerful, fade free and doesn't require a gorilla like grasp to employ the hydraulically actuated caliper. Front braking power is predictable and smooth. Coupled with the rear binder the chassis was amazingly stable during the braking tests when the machine was pulled down at 65 mph during our repeated panic stops. The only other bike we ever found as stable as the new 750 Yamaha was the Honda Four. To say the braking power of the new Yamaha twin astounded us must be classified as a gross understatement. We truly were not expecting the type of stopping power this motorcycle is capable of producing.

The forks themselves are of conventional design and utilize the same construction features found on a number of other Japanese and European products now offered for sale. The lower fork leg is cast aluminum with the fork slider sliding directly on the upper stanchion tube. This eliminates the need for special bushings, which were used previously. The only objection we had to the forks was that we felt the springs were too light. The same thing must also be said about the rear suspension. Up to about 75 mph the suspension is more than adequate, but above that speed we got the old twitchy feeling routine. This can be considerably minimized by having the rider slide back as far as possible. Adding a passenger also suddenly makes the chassis far more stable. It is our feeling that Yamaha would be wise to consider using heavier springs front and rear to help minimize this high speed wobbling we found once the machine exceeded 80 mph. A number of other Oriental road burners of the same displacement suffer from the same problem. In many cases (if not all) this problem has either been eliminated or drastically minimized by the addition of beefier spring units either on the front or back, or in many cases, both.

This twitching situation, believe it or not, is our only serious criticism of the entire product. As steady readers of CYCLE GUIDE already know, we are not bashful about saying something when something has to be said, even if it's unpleasant (and in many cases it is). We were quite impressed with Yamaha's latest offering, having had the opportunity of testing six other similar products at the same time.

Naturally with a motorcycle of this type the rider is vitally concerned with the power output and rightfully so. The big Yamaha won't let him down. Make no mistake—it's no drag strip scorcher. The interesting thing was that it felt a lot quicker than it really was. A good part of the reason for this feeling is the wide flat power curve and the more than ample output at lower speeds. While the machine did not run as quick as we thought it would, it did run very consistently. Virtually all of the ET's were within a tenth of a second of each other. The thing that did surprise us was that the trap speed at the end of the quarter was only 96-97 mph. We would have expected the big twin to run faster than that. It charges out of the gate like a shot (and away from the stop lights the same way), so all of you street racer types out there will have no trouble dispatching many other competitors when the light goes green at the traffic signal.

Another delightful surprise was the lack of vibration. At no time were we ever able to detect any objectionable vibration in the entire power train. It's as smooth as the Norton Commando, which up till now has always set the pace for twin cylinder smoothness.

A good portion of the vibration reduction can be traced to a pair of contra-rotating weights at the bottom of the powerplant. These chain driven weights greatly dampen the vibration expected with a vertical twin. It appears these weights can be phased to favor any portion of the performance scale, although as we received the bike the phasing more than did the job all the way from idle to the top end.

Naturally, with an engine with the torque capacity of this one you would automatically assume gearbox ratios are not vitally critical, and you'd be right in thinking so. Our impression is that a rider could get by with a four speed very nicely, but of course this is the age of five speeds. In order for any motorcycle to be considered up to date, the manufacturer deems it necessary to add that fifth gear. In the case of the Yamaha they didn't really need it.

The engine itself is a fairly conventional layout utilizing a single overhead cam with the conventional two valves per cylinder. The 743cc engine revs very quickly to 7000 where it's redlined. We found this to be the optimum shifting point on the drag strip. By today's standards the 8.4:1 compression ratio is a bit lower than we would have suspected. But with the massive low speed power output we certainly could not suggest raising it any further than it is now. The torque peak comes at 6000 rpm, and the engine is rated at 50.6 foot pounds. The figure Yamaha quoted to us on horsepower was 63 at 6500 rpm. This seems high, but if it is correct, it must be measured at the crankshaft and not the rear wheel. If the bike was capable of producing 63 horses at the rear wheel, it certainly would have gone a lot faster in the quarter mile than it actually did.

New this year is a separate starting motor which is completely different than the old XS model. We also found that utilizing the kickstarter was virtually impossible since it came in direct contact with the right foot peg thereby making kick starting the engine anywhere from difficult to impossible. This can be easily remedied by either removing some of the material from the kick starter lever itself or possibly moving the foot peg forward a quarter of an inch. There really is no reason to have things that tight. The conventional battery ignition system is utilized, and we found that the electric starter fired the engine within two or three revolutions, which is certainly as quick or quicker than most of your other large displacement road machines.

As might be suspected, the 3.7 gallon tank did not last a great deal of time while riding hard at high speeds. We averaged 31.6 miles per gallon for the entire period of testing. Naturally our mileage figure is considerably lower than the average road rider's would be since our testing includes many miles of very high speed riding, not to mention running up and down the drag strip. This does terrible things to gas mileage figures.

The same basic type of carburetor found on Yamaha's older XS model is now used on the new 750 twin. We couldn't find any of the older carburetion bugs present on the new model so we can only assume Yamaha and Mikuni have got the mixers pretty well straightened away.

Throttle response was smooth although in low gear it's still a bit touchy just coming off of idle. The wet seven friction plate clutch is big and strong. Our only objection was that it tended to drag a hair thereby making it almost impossible to find neutral at a standstill. With the engine shut off, locating neutral was never a problem, but with the power plant turning over and the clutch lever up against the handle, we were never able to click it into that elusive spot between low and second gear.

Shifting was always smooth with normal lever travel. We also noticed the clutch starting to take hold immediately after the lever started moving away from the handgrip. Engagement was a long gradual process.

Incorporated into the new design are a few trick features that show Yamaha's engineering department has not been idle in the past couple of years. Located on the rear backing plate there is a small switch that is activated when the brake lining wears down so far. After sufficient wear has occurred the switch is then closed, and a warning light appears on the instrument panel directly in front of the rider. Until the brake lining is replaced the light stays on, thereby always reminding the operator that the rear brakes are in need of attention. This year Yamaha has created a rather unique reserve lighting system. If either the low or high beam circuit is broken during operation, the reserve unit automatically cuts in the alternate circuit, and the other beam comes on. Also located on the instrument panel is a light marked -Tail Lamp."' Whenever the front hand brake or rear foot brake is activated, the light bulb automatically comes on showing the system is in good working order. Should the light bulb in the taillight itself malfunction or burn out, the tail lamp indicator on the instrument panel will inform the rider by flashing on and off. These are two rather unique innovations from a safety standpoint that we feel are very worthy of mention and are not merely gingerbread items to pump up the cost of the product.

From a noise level standpoint we were quite pleased to find that the Yamaha is extremely quiet and should have absolutely no trouble passing the California Highway Patrol noise test. The Yamaha 750 is second only to Honda for being the quietest super bike we've tested.►