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62 cmm January 2Ü11

Yamaha's RD125 twin is often overlooked in favour of its more potent RD200

sibling. But with a racing pedigree the early versions make fine projects, asserts.

Early In 1974 was probaoly the previous year with Swede Kent Andersson this used a vertically-split crankcase, a best time to be testing a high- taking the 125cc riders' championship? feature that was common at the time to all performance lightweight motorcycle. It was also one of a Yamaha range that of Yamaha's engines.

Even though the fuel crisis in the latter I regard as the last of the classic period The first high-performance 124cc half of the previous year had abated, for the factory. Styling was unpretentious (43 x 43mm) version of this engine with petrol prices had sky-rocketed and with peardrop fuel tanks, unfettered seats 15ps was used in the AS-1C in 1968

we were still crawling around under and enhanced by the big drum brakes but it wasn't until three years later in draconian speed limit laws. and the racing-look mudguard blades. 1971 that the familiar early-70s Yamaha

So if you were look ng for two-wheel In its performance the RD125 tw n styling appeared in the HX90 twin and kicks, why not try a Yamaha RD125 twin? was in many ways a miniaturized version also acopted on the AX125 twin for the

It was the quickest in its class, offered of the RD250 and RD350 twins launched Japanese market. For Europe the keen handlirg, could easily be:ter 60 miles a year earlier in the UK, but was based RD125 with the key reed-valve induction to the gallon, and cost just £304. Its rider on a different line of machines that system appeared alongside the bigger could also bask in a glorious racing image: originatec in the mid-1960s in Japan. Yamaha twins for 1974, replacing the

^ the factory had just launched its awesome On the domestic Japanese market, 90cc AS3 wi:h its conventional piston porting.

•j= TZ750 racer on which Giacomo Agostini machines were favoured, and with many Reed valves, with their engine-facing

^ wor the Day.ona 200 race in America. using single-cylinder engines, a twin lightweight petals, enabled longer c More thar three decades on, many provided a measure of sophistication. intake port timing for better peak power

-S will justifiably suggest that the RD200 Yamaha's was laurched for the 1966 without sacrificing flexibility becajse y twin, essentially the same machine with model year as the AT90 with a 89cc they essentially eliminated the blow

0 a much more potent engine, better brakes undersquare (36.5 x 43mm) two-stroke back that would otherwise occur at lower 5 and a self starter, is a far more exciting engine developing 3.2 ps (or Pferdestärke, revs. Yamaha called it Torque Induction. - option, and I'd not disagree. But back the German metric version of horsepower) Anotner feature that had become

(A then there was something exotic about and housed in a motorcycle with the typical universal on Yamaha's two-strokes was g the little Yamaha's pedigree: hadn't the gentlemanly-looking appearance of the day. automatic lubrication for the engine.

1 factory won three manufacturer's titles the As with all its derivatives up to the RD200, Rather than calling on the rider to mix oil

Final incarnation of Yamaha's RD125 twin (above) formed the basis of the lOOmph project (opposite) which was helped by ace tuner Stan Stephens (photo: Tony Sleep)

How could we wear this stuff?

One of the ringiest dings ol the 70s

Full complement of big bike clocks

Final incarnation of Yamaha's RD125 twin (above) formed the basis of the lOOmph project (opposite) which was helped by ace tuner Stan Stephens (photo: Tony Sleep)

with the fuel, oil from a separate tank was fed to the engine by a crankshaft-driven pump. Because the engine would also need to have the oil fed according to the load, an additional control to the feed was included. Clearly the engine wojld need more lubrication as more power was being prcduced, so a cable from the twstgrip cable cont'olled the pump stroke, and the amount of oil fed to the inlet ports. It wasn't as sophisticated as Suzuki's, which fed the crankshaft bearings directly, but it wo'ked reasonably well, if not necessarily preventing exhaust smoke at full throttle.

I first tested a Yamaha 125 twin, the RD125A for the weekly paper Motor Cycle early in January 1974 and I was hugely impressed by its performance and handling, particularly because I'd tested a similar talian Benelli twin three months earlier.

With a top speed at MIRA of 78mph, the Yamaha was almost lOmph faster than the Benelli and could in fact cruise at nearly 65mph with a fully kitted rider. Acceleration was way ahead cf any other 125cc machine though it was necessary to keep the engine rew ng in its power band above 7000rpm to give its best. It felt just like you imagined a racer would be.

And that was the thrill of ricing the RD125 twin. With claimed peak power of 16bhp at 9500rpm end five speeds to play with, you had to dance on the gear pedal to keep the revs up. That was when the character of the bike came into tocus and the fine pitch to which the taut suspension, keen roadholding on grippy tyres and the

How could we wear this stuff?

Full complement of big bike clocks

125's riding position didn't teel much different from my own RD250, though a glance at the smaller faces of the instruments - both a speedo and rev meter were provided - and the slimmer fuel tank were constant reminders. For some reason Yamaha fitted a friction damper to the steering head, controlled with a large plastic bezel. Perhaps the only time you'd need it was when carrying a passenger - the seat was just long enough though the pillion pegs were |nounted on the swing arm - when the fHant end would lighten dramatically.

^nugh the RD195 test bike had been fittecraith a kpn speedo, suggesting it was fr^k the French market, it did have the corr^^taller gearing for the UK with a 36-tooth mar sprocket rather than a 38-tooth iteim

For a 125, acceleration was sizzling, the bike despatching M RA's quarter mile test strip in 18.7 seconds with a terminal speed of 68.8mph. Time to 60mph from a standing start was 12.5 seconds. For a comparison, Honda's four-stroke single CB125J in 1976 clocked 19.45 seconds and 62.5mph while a full-power liquid-cooled RD125LC with 20bhp in 1983 clocked 17.1s at 73mph. ►

stopping power from the big drum brakes had been tuned was best appreciated.

Weighing just 2481b with a gallon of fuel, the RD125 could be flicked through bends as quickly as thinking about it, yet the steering was positive, like a highly-strung racer. The frame was typical of the period, with a simple tubular steel loop connecting the steering head to the swing arm pivot (with its outboard bushes) and the engine completing the connect on to the front down tube.

The only time I had any qualms about the bike's behaviour was when negotiating bumpy high-speed bends when the damping of the rear shocks would be overwhelmed, allowing the back end to squirm. Grip of the skinny Yokohama tyres - 2.50x18 front and 2.75x18 rear -was surprisingly good, as I recall.

Yet the bike was a model of refinement, for the period. It was so easy to start with the lever, you could do it by hand. For less frantic use the engine would pull from 2000rpm though with not much conviction and 3000rpm was necessary for a bris< start and to keep up with town traffic. Apart from a minor tremor a: about 5000rpm the engine was utterly smooth.

With its raised handlebar and footrests just forward of the long seat's nose, the

One of the ringiest dings ol the 70s w}/vw.classicmechanics.com emm 63 Release: StoreMags & Fantamag. Magazines for All

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