The rise and fall of the two-stroke

Honda NSR500 engine front Honda Collection Hall CREDIT Morio Creative Commons2

Published on 2 October 2018 by Matt Colley

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Filed under Category: Features

Two-stroke road bikes were a dominant force in the ‘70s and ‘80s, but then they disappeared. In an article that first appeared in the Autumn issue of the BMF's magazine Motorcycle Rider, Jeremy Pick looks at the enduring appeal of the ‘stroker’ and examines some of the key bikes that made the two-stroke legend...

They’ve powered some legendary motorcycles. They dominated track and off-road racing through the ‘70s and ‘80s. They are quick, light and noisy, and have powerbands that have launched endless pub conversations.

Yes, there’s something visceral about a big two-stroke motorcycle. The smell of two-stroke oil in the air and the sound of two-strokes tearing down a track or a road are sure to spark nostalgic memories to those riders of a certain age who cut their teeth on Yamaha FS1s and Suzuki AP50s before moving onto two-stroke 250s.

The secret of the enduring appeal – and ultimate demise – of the two-stroke lies in the engine design itself. Two-strokes use ports in the cylinder walls to transfer the air-fuel mixture into the combustion chamber and the exhaust gases out. Because a two-stroke delivers power with every crankshaft revolution, instead of every other revolution as is the case with a four-stroke, the power delivery is significantly higher than a similar capacity four-stroke.

On the negative side, two-strokes have short service lives, a reputation for fragility and, worst of all, terrible emissions. The latter is especially bad because the exhaust and intake ports are open at the same time; raw fuel mix can flow across and get into the exhaust. Consequently, modern emissions laws have seen a drastic decline in the use of two-strokes and most are now found in off-road competition bikes and scooters.

Modern technology means there are now ways to reduce two-stroke emissions, but few manufacturers are willing to invest in the R&D required. One of the rare few is KTM, with a direct fuel injection system fitted to their off-road two-strokes to give wide power delivery, low fuel and oil consumption, easy cold starts and no need for adjustments for altitude. Few other manufacturers look set to follow suit.

Today, nostalgia and the recognised importance and performance of the key bikes make many two-stroke models highly collectible. It now seems like everyone wants a big road two-stroke, so the demand in the used two-stroke market has been rising rapidly over the past few years. If you also yearn for a large-capacity two-stroke, Rider looks at some of the best available options:

 

Yamaha RD350
A cult bike if there ever was one. The original RD350LC was the ultimate budget racer and hooligan street bike during the mid-70s. Lightweight, fast, relatively reliable and easily modified, the little RD could beat and out-brake just about anything up to 750cc. A frame based on the TZ race bikes, a six-speed gearbox and 39bhp at 7,500rpm were unheard of at the time. The ‘RD’ name even became known as an abbreviation of ‘Rapid Death’ – perhaps unfairly – due to the number of accidents.

Now recognised as a classic, the few remaining examples that haven’t been thrashed to within an inch of their lives fetch good prices on the used market thanks to those who want to recapture the excitement of their youth.

Suzuki GT750
Affectionately nicknamed ‘the Kettle’ in the UK, the three-cylinder GT750 was one of the first big Japanese motorcycles with a water-cooled engine when it launched in 1971. Initial models saw braking at the front taken care of by twin leading shoe drum brakes (these alone are highly desirable today), but they were quickly replaced by twin discs – another first.

Despite being so far ahead of its time, the GT750 fell victim to the stricter emissions regulations of the late ‘70s. Tuned for torque rather than power and with a modest compression ratio, the GT750 was a true two-stroke Grand Tourer rather than a hooligan bike. Prices have risen in recent years, so expect to pay from £6,000-£12,000 depending on condition.

Kawasaki 500 H1/750 H2
Kawasaki’s three-cylinder 500 H1 was a revelation when it appeared at the very end of the ‘60s. A high power-to weight ratio, a vicious powerband kicking in at around 5,000RPM and generally poor handling and braking created a fearsome reputation and gave Kawasaki a high-performance bad-boy image. It quickly became known as ‘The Widowmaker’.

In 1971, the 750cc H2 was introduced with some of the handling issues and narrow powerband of the H1 addressed. No other bike available at the time could even approach its performance – a standard bike could cover the standing quarter mile in 12 seconds – and it made a serious single-handed contribution to the decline of the British motorcycle industry itself.

H1 prices start around £7,000, rising to double that or more for a mint example. Meanwhile, you can expect to pay £12,000 and up for a decent H2, and potentially much more depending on condition and originality.

Suzuki RG500 Gamma
Launched in 1985, the square four ‘Gamma’ was based on the all-conquering Suzuki 500 GP  race bike made famous by Sheene, Mamola and seven consecutive constructor wins. Performance and handling was exceptional for the time, with performance really kicking in above 7,000RPM and rising to 12,000RPM. With its aluminium box section frame and cassette gearbox, the Gamma was seen as one of the best of the later two-stroke designs. The significance of the race bike it is based on means that prices have been accelerating sharply in the past few years, so expect to pay £12,000-£20,000 for a good example.

Bimota V Due
The bike that killed Bimota. The boutique Italian marque launched the V-twin two-stroke V Due in 1997 with the aim of revolutionising sports bikes, and the technical specs included direct fuel injection and a promising GP performance for the street.

Unfortunately, the production run was plagued with issues that led to many owners returning their bikes. Bimota never managed to resolve the fuel injection – for a while, models were sold with carburettors in an attempt to resolve the fuelling issues – but the costs involved overwhelmed the company and it went into liquidation in 1999.

Ironically, the issues have now been resolved and existing bikes now have a cult following. Remaining examples now reach stratospheric prices.

Aprilia RS250
Launched in 1994 and based on the MotoGP bike ridden by Rossi and Biaggi, the RS250 is now recognised as one of the finest-handling bikes of all time. The little V-twin is an uncompromised sports motorcycle wrapped in a beautiful package and was the poster bike for a generation of aspiring young riders. Very collectable indeed today, good examples still exist at a reasonable price – for now.

Where to find a bargain
With prices for the true classics already very high and set to rise further, the best opportunities in the two-stroke market are at the smaller capacity end. The Suzuki GT500 is still available at reasonable prices, as are the Suzuki GT185 and Yamaha RD200. Italian two-strokes are also worth considering while prices are low – Aermacchi and Cagiva 250s are looking like good bets. So long as you are happy with the performance trade-off inherent in smaller bikes, smaller capacity Japanese and Italian two-strokes, mopeds and off-road bikes are worthy of consideration too.

Did you have or do you have a two-stroke? Share your memories and stories on our Facebook page.

 

Picture credit: Morio, Creative Commons