Like Kawasaki’s KH and suzuki’s GT, Yamaha’s RD came to define the “tuning fork brand” for many riders and the mid-weight twins have attained cult status.
Yamaha’s first 2-stroke twin was the YD-1 of 1957 but the 250 and 350 RD twins were direct descendants of the YDS7 and YR5 respectively. Eventually the 350 would evolve into the mighty RD400 before water-cooling and the LC series emerged, but the sheer simplicity of design, relatively low cost and amazing performance of the RD twins means that, even today, they are a practical classic that can surprise modern traffic.
The first RD’s in 1973 came with reed valves, a way of metering the fuel air mixture via the intake draw of the engine in order to produce more torque (hence the side panel wording “Torque Induction”). At 39hp for the 350 and the high 20’s for the 250, the engines were certainly efficient and lively performance was easily attained. Gradual refinements included a surprisingly efficient single piston front brake and the adoption of six speed gearboxes.
In 1976 the RD350B made its last appearance in the Yamaha line up though it did not disappear entirely continuing to be manufactured in India for some years under the Rajdoot name. Both the RD250 and the new RD400 came with a boxy “coffin” tank, discs front and rear plus the option of cast aluminium wheels; the first machines to have them.
The following year both machines sported a rear “tail cowl” and continued to exploit the “speed block” style graphics initially seen on Kenny Roberts’ TZ racers.
Eventually the 1979 models of both the 250 and 400 were fitted with electronic ignition and, along with other mods to footpeg mounts for the rider and exhaust fittings, this was the zenith of Yamaha’s mid-capacity RD twins.
issued: Friday, March 24, 2023
updated: Tuesday, March 28, 2023
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