Click above for more shots of the Greenfly LPG motorcycle

Liquefied Petroleum Gas, or LPG as it's more commonly known, is derived from fossil fuels, but it also burns significantly cleaner than other petroleum-based fuels and has a higher octane rating. In fact, LPG produces 19 percent less carbon than oil as it burns and is free of particulate matter. So, why aren't we all filling our cars' tanks with propane or butane? There are a few reasons, not the least of which are its need to be compressed and stored in heavy containers and its comparatively low energy density when compared to gasoline means that more fuel is used to get any given distance.

Despite its drawbacks, the fact that LPG burns clean and is usually quite a bit cheaper than gasoline or diesel makes it an attractive choice for many, including a man by the name of Dave Akhurst, who engineered and built his own motorcycle that runs on LPG from a Yamaha XT500. A high-pressure tank holds the LPG under the rider (hm, safe?) and the 500cc single cylinder engine reportedly gets about 70 miles per gallon of LPG and makes about 30 horsepower. There's lots more to take note of here, including the single-sided swingarm and fork, automatic transmission with belt drive, hand-made body bits and panniers and awesome 3-piece custom wheels. This is some seriously good craftsmanship.

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[Sources: The Biker Gene, MOTORRAD]