Pretty much everyone expected the RD250/350LC to be the last gasp of the performance two stroke, but they were wrong. In 1983 a thermostat was fitted, which cured the ailment. The first model RD350LC was not fitted with a thermostat however, and in cold European weather, had trouble reaching an optimum operating temperature – a problem many riders address by the expedient of applying tape to the radiator to raise the temperature. The water-cooling of the RD/LC was a big selling point, with finer tolerances achieved as a result of a more stable engine temperature. With the Japanese ‘big four’ all producing road-going two strokes, variants of the YPVS system caught on rapidly from the time it first appeared on the revamped LC models in 1983. As revs increased, the engine’s CDI unit allowed the valve to rotate to a fully open position at maximum revs. In California, measures went even further, with a third converter in the header pipes and a carbon canister inside the fuel tank to capture vapour before it reached the atmosphere.įor the 1980 Grand Prix season, Kenny Roberts’ works YZR500 was fitted with what Yamaha called YPVS – Yamaha Power Valve System – a rotating cylinder fitted across the engine’s exhaust ports which was controlled electronically to vary the port timing and increase power and torque – and burn the mixture more completely. When combined with oxygen, the converter essentially ignited the unburned fuel mixture that had passed through the engine. In fact, the RZ350 (as it was sold in US) did not appear in the American market until 1983, and only then with the addition of a catalytic converter in each muffler of the exhaust system, and with no adjustment possible within the carburettors to deter home tuners from fiddling with the factory settings. Again, it was US emission laws that sounded the death knell. The 350 went on sale in Australia in 1981, priced at $2099, and continued until 1986, during which time it subtly evolved into the form of the bike featured on these pages. RZ350 in a Sydney dealership, circa 1984. Getting the expansion chamber exhaust to stay in one piece took a little longer. There were also persistent mid-range performance issues – a combination of cylinder design and carburation settings, with both these original components replaced in the next model, along with a redesigned reed valve and a new design of oil pump. Vibration was the main culprit, causing exhaust pipes to crack and exhaust mounting studs to break off. But the 350 in particular was not without its problems, which began to show up immediately, especially under racing conditions. It took a few months longer (until mid 1980) before the model began appearing in showrooms in Europe, in both 250cc and 350cc form, and with twin front discs, where they were eagerly snaffled up. The new roadster sported a single disc brake up front and a drum rear brake. RD250LCs line up for practice at Bathurst in 1981.Īs shown in Paris, the LC (Liquid Cooled) sported the Monoshock cantilever rear suspension originally conceived by the Belgian designer Lucien Tilkins, and which had graced the TZ range since the C model of 1975. Naturally, this point was not lost on legions of aspiring play racers, who saw the new RD350LC as the answer to their prayers – a weekday ride that could more than hold its own on the track on weekends. It’s just that the ‘LC’ (the RD bit was a tilt to the now-defunct air-cooled RD range which had run up the white flag in the battle against ever-tougher emission laws) was such a complete package – the prodigal son of the racing TZ stable that had powered privateers and works riders alike since 1972, and without which, racing would have struggled to survive. But it wasn’t that revolutionary, after all, Scott built the same thing more than 50 years earlier. Story and photos: Jim Scaysbrook When Yamaha trotted out the RD350LC at the Paris Motorcycle Show in 1979, it was hailed as a miracle of modern engineering – a water-cooled twin cylinder two-stroke. From our Old Bike Archives – Issue 71 – first published in 2018.
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