"INTRODUCTION Carburetor throttle body deposits normally form during engine idle periods when the throttle plate is nearly closed. Because of the small space between the throttle plate and the throttle body@ air entering the engine passes this point at a very high velocity. Any contaminants contained in the intake mixture tend to be centrifuged out and deposited on the throttle body. In addition@ blowby gases flowing into the intake air stream under certain conditions (as may be caused by a plugged PCV valve) tend to accentuate the deposit problem. Crankcase blowby is also conducive to deposit formation in the PCV valve. Although considerable work has been done on the effects of lubricating oil@ oil drain periods@ and fuel additives on PCV valve and carburetor cleanliness@ very little information had been available on the effects of fuel additives as they relate to exhaust emissions. In order to determine the magnitude of these effects@ controlled field testing under realistic conditions was necessary. This report presents a discussion and the results of a program to determine the ""Effects of Gasoline Additives on Carburetor and Positive Crankcase Ventilation System Performance As They Relate to Exhaust Emissions."" The first year program was conducted under a research agreement between Scott Research Laboratories@ Inc. (Scott)@ and the Coordinating Research Council@ Inc. (CRC)@ covering the period from February 1@ 1969 through March 31@ 1970. During the same period Scott conducted a supporting program under Federal Contract CPA-22-69-47. The results of the first year program were reported in a report prepared for CRC and the Department of Health@ Education@ and Welfare (DHEW) entitled ""Effects of Gasoline Additives on Carburetors and PCV System Performance As They Relate to Exhaust Emissions."" A second year program followed with a research agreement between Scott and CRC dated February 15@ 1970. The expiration date of this agreement was advanced by CRC from December@ 1970 to December@ 1971. The work was conducted in support of CRC/APRAC Project Number CAPE 2-68."