Occasionally, we come across a technology that has just kind of been forgotten about. Take this Ural motorcycle. It runs on a substance called wood gas, which is the byproduct of incomplete combustion of carbon products like wood, hence it's name. The fuel goes through a process called gasification in a wood-gas generator to produce combustible hydrogen and carbon monoxide. So basically, you're burning wood to produce fuel.
This Ural has had a rudimentary wood-gas generator fitted, while an a number of other low-tech, scrounged items make up the rest of the side-car-mounted system. According to The Knee Slider, the top speed of the bike is a mere 80 kilometers per hour (about 50 miles per hour), while the fuel it runs on is quite bulky. Still, if you run low, just pack an axe and hope you run out of gas somewhere that's wooded.
Wood-gas-powered vehicles might be uncommon today, but they were a normal means of transport in the past. Vehicles in Germany, Sweden, France, Denmark, Switzerland and Finland were converted to run on wood gas during World War II due to fuel rationing, while wood-gas is still used in rural parts of the world today. Take a look at the wood-gas Ural in the gallery provided by English Russia.