Towards the late 1960s Yamaha was winning grand prix (GP) races with their factory air-cooled two-stroke racing motorcycles, easily beating four-stroke machines with larger displacements.
In 1969 Yamaha introduced production racing motorcycles based on their GP racers but available over the counter to customers. These proved very popular in senior and open class racing. This was a clever way of marketing their brand with the ordinary man on the street being able to access a GP replica for under $2,000 (Sh13,800 at 1973 prices).
I remember in 1972 Vic Preston Jnr. and John Lyall campaigned the Yamaha TR3 350cc production racers on the Embakasi and Nakuru race tracks obliterating the traditional four-stroke Norton, BSA and Triumph competition. Of course, my diminutive clubman’s Yamaha 200cc was no match for these purpose-built machines but I never suffered the ignominy of being lapped by any of them.
Elsewhere in the US, Don Vesco won the 1972 Daytona 200 on a Yamaha TR3 the first two-stroke and the smallest displacement motorcycle to win at Daytona. Two-strokes would continue to dominate road racing until 1985 when the rules were changed.
In 1973 Yamaha introduced a completely new street motorcycle, the RD350. It was not a totally new model, but an evolution of the 1970 R5, itself a big improvement on the cumbersome and ugly YR-1 of the 1960s. The RD350 came with a dual-piston front disc brake, close-ratio six-speed gearbox, and reed-valve intake system labelled “Torque Induction” by Yamaha marketeers.
The difference between the R5 and the RD was most obvious in performance. The RD zipped through the quarter-mile over a second faster than the R5, with 9 miles per hour (mph) more in terminal speed-14.3 seconds and 89.8mph. The RD was said to be the hardest-stopping street-bike money could buy at the time and at $900 (Sh6,200 at 1973 prices), was truly affordable.
With 39 brake horsepower (bhp) at the crankshaft and a kerb weight of only 155 kgs the RD possessed an awe-inspiring power to weight ratio making it the best “wheelier” of all time. This brought out the hooligan in many young riders of the time who would often be seen popping wheelies almost at will.
The RD excelled in the real world especially if your world consisted of twisty roads where an aggressive RD rider could wreak havoc on bigger motorcycles of 750cc and above earning the moniker the “Giant Killer”. Balance was the key. Instead of high technology Yamaha engineers depended on years of experience gained from building road racers that had thoroughly dominated the 250cc and 350cc classes worldwide. The RD engine cases could slip straight into the TR3 road racers which had similar dimensions. However, the RD frames received extra bracing and gusseting in the high stress areas around the steering head, engine mounts and swingarm resulting in a frame which did not flex, wobble or shimmy when a rider pointed at an apex, making it one of the most sure-footed motorcycles of the time. While it could turn corners quicker than a mouse in a maze, the only limitation was the footrests which tended to scrape the ground when the machine was leaned over.
Within days, it seemed, an entire cottage industry catering exclusively for the little roadster sprang up, and RDs sprouted expansion chambers, carburettor adaptations, low-slung handlebars, fibreglass fairings, seats and tanks, and all manner of custom porting jobs to wring even more power out of the engine.
With EPA and clean air closing in during the mid-1970s, it was only a matter of time before the two-stroke motorcycle became a two-wheeled dinosaur. But in 1976, Yamaha fought back with the RD400C.
While the 400C was essentially a brand-new motorcycle. Its lineage was plain to see with bore remaining the same at 64mm while stroke increased to 62mm. Bypass holes in the cylinders and cutaways in the piston skirts reduced low-end surge and silenced the engine at lower rpm.
The RD400C became the first production motorcycle to be equipped with alloy wheels as standard. Both front and rear wheels were fitted with identical disc brakes while suspension was improved all round and the famous “coffin” fuel tank was adopted. The engine was moved slightly forward in the frame allowing for a larger airbox while the footrests, engine and handlebars were all rubber mounted to reduce vibration.
The RD was as popular as ever. Death was imminent though.
One year before the EPA edit of 1980, Yamaha sprang the RD400F Daytona complete with emissions-control valves, chassis upgrades, a restyling job with Euro-style fuel tank and finally the footrests were moved up from under the exhausts.
Even running a bit cleaner (and suffering at any throttle opening other than wide open) the RD400F was still good for 14.18 and 91.4mph at the dragstrip.
The RD400F was the last air-cooled RD.
A water cooled RD350LC was introduced in 1980 but by that time four-stroke engine development had greatly eroded the advantages of the two-stroke in addition to the tightening of emission controls and its inherent thirst for fuel. Ultimately the RD was discontinued in 1986 but some units were produced in Brazil until 1995.
Are we likely to see “big bore” two-strokes on our roads again? There have been great advances in electronic fuel injection in the automotive world which makes clean-running two-stroke engines feasible. KTM recently introduced a new line of fuel-injected off-road motorcycles that aim to deliver the benefits of the engine namely, raw power and light weight, while minimising high emissions and fuel inefficiency that have sidelined the technology.
I joined the “hooligan” brigade in 1980 when I purchased the RD400G (non-USA model) which I still own today.