While Boston-area racers were making do on spindly Yamaha TD1-Bs and Cs with their seal-blowing forks, cracking brake-drum liners, and fatiguing engine mounts, we could read in the magazines about the RD56 factory 250 racer on which Phil Read was world champion in 1964 and ’65. It was everything our bikes were not. It had an uncompromisingly racy twin-loop frame, a rotary-valve engine making almost 20 hp more than our production-derived piston-port engines, and it had a lovely four-leading-shoe brake.
We hadn’t long to wait. In 1969 all of the RD56′s chassis virtues arrived with the new Yamaha TD2, plus a feature even RD56 lacked: four transfer ports per cylinder, in a complete departure from the classic three transfers of the past. Those four transfers stand comparison with the best of subsequent design.
It was beautiful. I well remember the intake of breath that came as we pulled away the side of the crate. The long, squared-off-looking fuel tank. The giant four-shoe front brake. The luster of polished aluminum rims. The pair of 30mm Mikuni VM carbs, carried in vibration-quelling rubber mounts. Everything purposeful, and few vestiges of production origin. Yes, there was still a kickstarter, but I had plenty else to feast my eyes upon. Feasting, feasting.
Yet when, 25 years later, I was summoned to see 10 nicely restored TD2s assembled for 250 Daytona vintage practice, it could not “take me back.” In 1969 those bikes were ridden by future champions, tuned by hands happy to accept the possible consequences of jetting to peak power.
These nice-looking restorations made the right sounds and sights, but were animations of the past. As with first love, I could not repeat the surprise and delight of opening that crate.
Among four-strokes, who could not have delighted in the constant evolution of ultra-high-rpm GP roadracing engines from Honda, 1959-1967? When I first saw a small photo of the RC160 in an English auto mag, I was enthralled by the existence of a four-cylinder 250. When I visited Japan in February of last year, there it was in the entranceway of the Honda Collection Hall in Motegi. Not a single one of those engines was designed by The Egg Man, that evil genius who decided engine crankcases should be “styled” rather than looking like aluminum was shrink-wrapped over unseen moving parts.
Under the screen in front of me is a cylinder stud made for the Kenny Roberts Team V5 990s. As with so many beautiful parts, whether living or created by human design, its shape arises from its function, from the purposes it serves. I keep this and many other machine parts at hand because of what they have taught me.
We sold Triumphs and Kawasakis from our dealership, opening on April Fools’ Day, 1969. Always a part of setup was the first engine start. Every twin, in that moment, showed life by the rapid fore-and-aft shaking of its front wheel. Sportsters did it too. When, once every few years, I chance to see a classic Triumph 650 running, I stand next to it, drinking in that spectacle of shaking. With both pistons moving together, a 650′s vertical shaking force would have been unbearable at the best-compromise balance factor of 51 percent of the reciprocating mass. The engine, sitting on two curved and flexy steel tube frame loops, would set them vibrating like that front wheel, numbing hands, feet, and butts around the world. To avoid that, the balance factor was pushed as high as 85 percent. That shifted the shaking force from vertical to horizontal, saving the rider from the worst of it, and instead driving the front wheel into its frenetic dance. So I treasure that motion when I see it, for the story it tells.
Another time I would be treated to the general case of sympathetic vibration. Robin Tuluie, then working at the vehicle testing firm MTS in Minneapolis, showed me a Yamaha 750 production bike on a two-post shaker (each wheel rested on the end of a hydraulic actuator that could be driven over a range of frequencies). As he ran those pistons through a frequency sweep, I could see first one, then another and another part of the machine excited into its own motion. At 23 cycles or so, the front wheel was moving so fast and so far that it became a blur. Older riders have seen shift pedals almost disappear in a particular range of rpm, piston shaking force taking the place of those hydraulic actuators. Kawasaki at one point had to increase the diameter of the shift shafts used in its three-cylinder race engines to prevent that vibration from breaking them.
Why “older riders”? Because in recent years new engines are designed around stopping vibration at its source with “counter-shakers”—spinning eccentric weights on gear-driven shafts, sized to cancel some or all of primary and/or secondary vibration. Some older riders miss the vibration, secretly wishing moderns would “man up “and join them in heroic numbness. Younger ones have never known raw engine vibration; when given a ride on an older bike they ask, “Are all of them that bad?”
When steam locomotive builder Baldwin-Lima-Hamilton needed means by which to study the track-destroying effects of primary imbalance, it found nothing on the market. It therefore bought a small strain-gage manufacturer and developed its own electronic data gathering instruments. When BLH built its last steamer, in 1956, the only part of the company that remained viable was instrumentation. I would use BLH chart recorders at work in the mid-1960s.
I love the look of engine intake systems. Look down at the densely packaged carburetors of a Honda RC30 V-4 and turn the throttle. I imagine myself as molecules of oxygen or fuel, about to accelerate into those hungry bellmouths.
After synchronizing the throttle slides on a Kawasaki H2R 750 race engine, I liked to stare a minute at the upturned carburetors as their slides rose and fell with my turn of the throttle. In my mind, this sight had abstract, mysterious power. It still does.
Just as I no longer wish I were in my shop on a cold January evening, trying to make the choke pull-off system of my wife’s Oldsmobile wagon work (“bend lever C to match diagram 22”), so I also no longer yearn to be changing jets at trackside as the sun warms the air from morning to noon. In the 1980s you could walk past race team transporters in paddocks and see, in their dense shade, barometer, thermometer, and humidity gauge. Soon they were replaced as guides to correct jetting by air density meters, but the process of removing carbs from engines, draining their fuel, and changing jets to correct fuel-air ratio continued. And what about production bikes? In those faraway pre-emissions days, carburetors just ran rich in summer and lean in spring and fall, with attendant predictable power loss as compared with correct mixture.
Then came automotive-style digital fuel injection, controlled by on-board versions of the instruments just described. Let tempest storms of wind or changes of altitude come and go—digital fuel injection continuously keeps fuel-air ratio where it belongs. Yet I do remember peering into spark plugs as Champion’s Bobby Strahlman taught us all to do, looking for the visual clues that would guide us toward maximum-power mixture and spark timing. The sight of a spark plug is trigger enough.
For a time, the cold-start enrichment systems of fuel-injected bikes remained as crude as in carburetor days, in concept no different from putting your hand over the carb intake while turning the engine. This “choking” pulled in a huge amount of fuel, enough that evaporation of just the most volatile 10 percent of it could be spark-ignited.
But then the spoilsports gave engines motor-driven throttle positioners. I start the engine in my little car at zero degrees and revel in a steady 1,200-rpm initial idle. As warmth spreads from combustion chambers to the intake system, a larger proportion of fuel evaporates. The system simultaneously leans fuel delivery and reduces idle rpm. Civilization and its contentments! Yet still I remember those choke pull-off rods.
To me, the most beautiful of carburetors is the classic Amal GP. Too young to have worked with them, I still revere them for their functional shape and textures, plus their association with classic machines such as the Manx Norton and AJS 7R singles. I keep a GP carb to look at, and I have multicompartment boxes of Mikuni VM tuning parts just in case a reality glitch sends time backward.Source link