Motorcyclists who grew up in the ’70s and who had more than a hint of fire in their veins would have had to try a Yamaha two-stroke twin. In whatever size they came, from 125cc to 400cc, these bikes were fast and furious. Yamaha two-stroke twins could punch more than their weight and their image was enhanced by their close familial ties with Yamaha’s production racers. Not for nothing were Yamaha’s road twins prefixed RD, short for ‘race developed’, and the RD400 of 1976 represented the culmination of years of race development.
Agile, light, simple and reliable, the RD400 would take you from work and back Monday through to Friday, offering only the odd oil-fouled spark plug in protest. Smooth and comfortable enough for freeway travel, it had a complete change of personality when exposed to back roads. While motorcycle handling for other Japanese manufacturers was still an oxymoron, the RD set the standard and humiliated bikes twice its size.
The RD’s minimalist approach was more suited to eating up twisty pavement than straight stretches. Topping out around 170km/h it wasn’t the fastest bike down the straights, but it more than made up for it in the corners. The engine and frame were both born on the racetrack, derived from the 750-slaying TR2 production racer, but the street bike’s frame used thicker-wall steel tubing, still with track-spec geometry.
And while other Japanese manufacturers persisted with weak floating-piston brake callipers, Yamaha fitted the RD400 with a potent opposed-piston caliper. Even with only a single 270mm disc this brake could stand the 156kg RD400 on its front wheel.
The first production bike with factory-fitted, cast-alloy wheels, the RD400 provided racetrack performance for the masses. From its birth until Yamaha’s FZR400 took over in 1988, Yamaha two-strokes were the dominant tool for budget 400 proddie racing.
Yamaha created the 398cc RD400 out of the already impressive RD350 by lengthening the stroke 8mm, the 64mm x 62mm reed valve twin still fed by a pair of 28mm Mikuni carbs. With a six-speed gearbox the engine provided deceptive power over a wide rev range. The weight distribution favoured the rear and the RD400 could lift the front wheel from low revs with little effort. In the days of cheap petrol it didn’t matter if it was thirsty when used aggressively – what mattered was the RD gave the ultimate bang for your bucks.
But the writing was on the wall for the air-cooled two-stroke. Unburned hydrocarbons were about to become as politically incorrect as a triple cheeseburger high in saturated fat. The market demanded bigger, faster, and more sophisticated bikes, and that meant a four-stroke.
By modern standards the RD400 looks elemental and tiny. There were few concessions to comfort and practicality. The seat is hard, starting is by kickstart only, and the suspension rudimentary. But for air-cooled simplicity the Yamaha RD twins represented a pinnacle of design that in its day was unmatched for performance and style.
FACT FILE: Yamaha RD400
1. Grandfather to the RD, the 1967 R1 was Yamaha’s first 350. Although it produced 26.5kW (36hp), the oil-injected twin suffered from a terminal case of the uglies.
2. Our own Kel Carruthers switched to Yamaha after winning the 1969 250 GP crown on a Benelli. On a 44.1kW (60hp) TR2B he won the Road Atlanta road race national in 1971, beating a field of larger bikes.
5. The 1970 R5 350 was the first street bike derived from the TR production racers. The R5 evolved into the RD350 for 1973 and lasted through until the RD350B of 1975.
4. Although the RD400C appeared in 1976 it lasted only until 1980 as the RD400G. The 1978 RD400E featured CDI ignition and more power, while an RD400 Daytona Special was available in the US in 1979.
5. Emission and noise controls saw the demise of the air-cooled two-stroke at the beginning of the 1980s, but Yamaha continued to build liquid-cooled LC two-strokes for several years.
Many thanks to Allen and Lorraine Smith of the Australian Motorcycle Museum, Haigslea, Queensland for the use of the 1977 RD400D featured.