Liquefied Petroleum Gas-Powered Motorcycle Greenfly

Is LPG Power Third-World Or Realworld? Either Way, Green Is Good

By Alan Cathcart, Photography by Kyoichi Nakamura

How can you save the world? Dave Akhurst has his own idea. That's why the 57-year-old British precision- engineer built one of the world's first liquefied petroleum gas-powered motorcycles and christened it the Greenfly. He also painted it green. LPG is a by-product of crude oil refining, or can even be extracted from oil or gas streams as they emerge from the ground. Generating 20 percent less CO than petrol, and 2 percent less than diesel, it is one of the greenest fuels on the market.

That's why Akhurst took a Yamaha XT500 single and created a minimalist LPG-burning motorcycle around it. The big single acts as a central chassis component, suspended from a monocoque aluminum bulkhead that doubles as the oil tank, to which the rear subframe is also bolted. Said structure incorporates the LPG gas tank, and carries the offset upper rear shock mount. Akhurst made the shock from an Austin Metro car damper and a BMW coil-spring. The Greenfly uses a single-sided aluminum Mono-arm telescopic strut, pivoting on Teflon-coated bearings. And thanks to a carefully positioned centerstand, either wheel can be unbolted with a single Allen key and swapped for that spare in front of your knees. The finished product weighs 242 pounds wet.

Akhurst eliminated the Yamaha's five-speed in favor of a scooter-style continuously variable transmission. This required a major redesign. "I was going to use the original Yamaha crankcases," he says. "I made a new crankcase myself from a piece of aluminum." Moving from unleaded to LPG meant replacing the standard Mikuni carburetor with a modified American gas-calibrator, otherwise known as a mixer.

After lighting the Greenfly via kick-start, the engine settles to a fast idle, with a rorty blat from the exhaust and relatively little vibration. Twist that wrist and the Greenfly responds immediately with admirable pickup from closed throttle. There's no discernable difference between this LPG-fuelled device and the gasoline version. As a proof of concept, it's job done.

Steering is hyper-direct, with no bump-steer. Quirky suspension is surprisingly supple, keeping the bike quite stable at speed. One major asset of the Mono-arm front end is that you can make a U-turn in about the length of the bike. Steering gets heavier with speed, but it's very stable around fast turns for such a light, lean motorcycle. The only real negative is the CVT's absence of engine braking. You have to apply the Grimeca disc brakes quite hard to stop.

But those are minor details. What matters most is that all the novel aspects of Dave Akhurst's eco-bike come together pretty well. So, now what? "I'd like to see it or something like it reach the marketplace," says Akhurst, "not to get rich quick or save the world, but because we have to break out of the dead-end design path we've got ourselves into. People have told me the Greenfly's a third-world bike, but I prefer to think of it as an any-world bike. It's very fuel-efficient and clean, it uses 25 percent fewer parts than anything else on the road, and it's completely recyclable." Any takers?

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