The water-cooled 4-stroke XZ550 was the first Yamaha model to feature automotive-style downdraft carburetors, with the air cleaner box mounted atop the carburetors to take advantage of a direct path for the fuel-air mixture into the cylinders - a more efficient delivery than the sidedraft carburetors common at the time. However, the height of the carburetors and their airbox required Yamaha to design a bulky tunnel into the underside of the generous 17 liter (4.5 gallon) gas tank. The result was improved performance, and the bike’s distinctive large squared-off fuel tank.