Yamaha RD 350

Road Test 1974

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.

We use Champions in our shop because that company's local field representative can supply solid information and plugs in any size, type or heat-range. Champion L-3G plugs allowed the Yamaha to start easier and run under varied conditions for three weeks without once misfiring.

So what's the big deal, you ask. Just screw in the jazzier plugs, go on your way and stop ranting. It is no big deal, really, we suppose. But the economics involved are a classic example of any manufacturer's constant vacillating between cost-savings and quality. Better coils which would fire normal sparkplugs would cost the manufacturer maybe an extra buck each. And the unobtanium-alloy plugs cost the bike's owner that much extra each time he changes to a fresh set. That leaves the coil manufacturer and the spark plug maker pointing the finger of blame at each other, with the biker somewhere in between. If an extra dollar were spent on very many of the bike's critical components, it could sell for twice its present price. And that price is already overblown beyond recognition, as we will see later.

It really is grossly unfair to niggle about the quality of the coils for so long. There are many components on the RD 350B which are excellent. The alternator is the excited-field type, which means that its output is governed by the rate of battery drain. No fuel-eating power is generated without being used. With a capacity of 160 watts, the alternator is more than capable of powering the high—output coils that are put on the RD 350s by those who run them in production races. And finally the Yamalube automatic oil metering pump meters the prescribed amounts to each carburetor instead of on the street, garage floor, and rider's shoes as did many in recent years. The instruments are reasonably accurate, the finish quality is good, and the seat is just that right combination of resiliency and firmness. Our only real reservation about any of the RD 350B's external fixtures concerns the gonad-gouger Yamaha has made of the bike's locking gas cap.

As indicated by the performance figures and our comments about smoothness and relative quietness, we think that the Yamaha 350 twin engine has become a mature and settled powerplant, while by nature and heredity remaining a hard-nosed hotrod. Nonetheless, quality control problems still arise at times. Our first test bike suffered a big power loss when its second ring seized to the piston. The replacement was a rocket that fizzled only when ignition demand exceeded coil output.

As all enthusiasts who have visited a dealer's showroom this year have noted, the price of bikes (especially Japanese' bikes) has soared. Last year the price of a RD 350 was $839: now ,the virtually identical RD 350B is a staggering $121 1. But everything is relative. That price will buy you a stiff-legged road-sports machine whose engine produces almost 100 brake horsepower per liter of piston displacement, whose 10.35 lbs. per brake horsepower (at curb weight) make it accelerate with an authority that belies its displacement, and whose magnificent brakes will stop harder than every other vehicle on the street. If the cruel clutch of inflation has grasped you less firmly than most, buy an RD 350B for the ride of your life. And complain like hell about any little faults that show up until the dealer fixes them.

One last thing: if the kind of performance described above appeals to you, and if you think a 350cc-sized motorcycle will feed your particular rat, you better buy an RD-350B some time soon. Hot, perky two-strokes have a way of producing unburned hydrocarbons that the Environmental Protection Agency finds unattractive. When and if smog legislation is enacted, you can bet your bottom dollar that hi-perf two-stroke street machines will be the first to drop. So get one, as they say, while they're hot. It might be your last chance.