The effects of unleaded gasoline properties on the formation of carburetor deposits were studied by analyzing data from six field tests and by conducting a laboratory engine test program which investigated a wide range of gasoline properties. The results showed that increasing sulfur, nonbasic nitrogen, olefin, and existent gum contents and 10% and 90% evaporation points increased carburetor throttle body deposits. The most practical and economical way to control carburetor deposits is with the use of an effective deposit control additive. Such an additive can also clean up and keep clean critical areas of a new design variable venturi carburetor. Problems of measuring fleet fuel economy are also discussed.