A fuel-air mixture generator has been developed which allows a vehicle to be run on a chassis dynamometer under both transient and steady-state conditions on premixed homogeneous gasoline-air mixtures using conventional nonleaded gasoline. Under these conditions cylinder-to-cylinder-variations of air/fuel ratio, and of carbon monoxide emission from a 90 cu in. 4-cyl engine were virtually eliminated, and variations of NO emissions were greatly reduced. However, variations in hydrocarbon emission were scarcely affected. With the premixed charge the vehicle could be run on an extremely lean air-fuel mixture, while retaining good driveability. At an air/fuel ratio of 22.5/1, CO and NO emissions over the U.S. Federal cycle according to the 1970 test procedure were 2.7 and 0.4 g/mile, respectively. However, unburned hydrocarbon emissions exceeded current legislative requirements.