You want speed-blocks and air-cooled two-stroke fun? You want an RD250/400
Yamaha’s air-cooled two-strokes can fling open the door to Funland – if bought cannily
There’s just something about an air-cooled RD Yamaha. Perhaps that’s because nearly everyone of a certain age owned either an RD250 or 400 – often both – or at least had a mate who had one. The middleweight RDS sold in their thousands and offered (relatively) cheap performance with more than decent reliability. Keep an RD250/400 in stock trim engine-wise and it would rarely let you down.
The RDS are children of the ’70s. The 250 replaced the YDS-7 in 1973, with the 400 arriving in ’76 and production ending in 1979 for both models. Flash, cool and fun, the two RDS fitted the decade perfectly.
The RD250 was the learner bike of choice for thousands. Good for around 90mph with the rider flat on the tank, the RD handled at least as well as the best of its competitors and, with the well-proven Yamaha Autolube system looking after the lubrication, proved a dependable package for new riders. UK owners had to make do with five ratios until 1975, when sixth gear was finally enabled – it had been there all the time, blanked off. But right from the start the RD was an exciting proposition for any red-blooded lad (or lass) starting out on two wheels.
It was – and remains – a good bike for the budding home mechanic, too. Horizontally-split crankcases with pins in the main bearings to locate them positively and ribs on the seals that locate in grooves in crankcase faces make engine rebuilds relatively straightforward. Engine parts are readily available and, although you might
have to use some pattern parts, an RD250 or 400 should be easy enough to keep on the road.
The RD400’S longer-stroke engine develops nearly 50% more torque than its smaller sibling – 30.31lb ft at 6500rpm, compared to the 250’s 20.9lb ft at 7000rpm. It’s also quicker at the top end and a good one should ease over the ton – just. RD400S cleaned up in production racing back in the day, while Bike magazine pronounced that it was ‘the optimal air-cooled twostroke’. Who are we to argue?
If you’re not a fan of the angular, post-1975 styling, you probably weren’t into bikes in the ’70s. It’s one of the iconic designs of the decade and – along with the inspired ‘speed-block’ graphics – still looks fresh and achingly cool today. Take a ride on a speed-block RD today and check out the reaction from passers-by if you’re in any doubt about that.
That’s the real reason for owning an RD250 or 400 today – riding one. Probably a 1978 or ’79 model with electronic ignition – and a bit more power in the case of the RD400 – is the most practical choice. However, some prefer the slightly quicker pick-up of the points-equipped bikes with their lighter alternator rotor. With modern tyres, the handling is way better than many other ’70s survivors and the disc brakes are pretty decent, too. They’re not stupidly fast, although even a 250 will cruise at 70mph, but the fact is, RD250S and 400s are ridiculously good fun. Whether you’re screaming the nuts off a rev-hungry 250 or surfing the surprisingly fat wave of torque on a 400, you’ll be grinning inside your crash helmet. Isn’t that what it’s all about?