Like the original YA-1, the Moegi runs on an air-cooled, 125-cc engine, which connects to the bike's 20-inch rear wheel with a simple belt drive. But engineers replaced the YA-1's lawnmower-like two-stroke with a low-friction four-stroke. They also incorporated another Yamaha invention: the DiASil cylinder, the world's first mass-produced all-aluminum, die-cast motorcycle cylinder. The DiASil's abrasion-resistant aluminum alloy dissipates heat at three times the rate of steel. When the engine isn't being adequately cooled by the wind (for example, when riding uphill or stuck in traffic), there's less power loss resulting from increased engine heat.