Ardisam imported into the U.S. engines not covered by an EPA-issued Certificate of Conformity (COC) because they did not conform to the design specifications in the application for the COC for engine family ACGPS.1591PA with respect to the carburetors and the rated power output. Specifically, the carburetors were found to have an adjustable idle mixture screw (covered by an easily-removed cap); whereas, the application for the COC for this engine family does not identify such an adjustment. When present on an engine design, adjustments such as these must be described in the application for the COC, along with a description of any means to limit such adjustment. Also, the maximum power output listed in the application for the COC was 2.7 kilowatts (kW) at 3,600 revolutions per minute (RPM), but the engine manual and documentation provided by Ardisam to U.S. Customs and Border Protection as part of the entry package lists the maximum power output as 3.7 kW and 5.0 horsepower at 3,600 RPM. A COC only covers engines that are materially the same as the engines described in the application for the COC. The presence of an adjustable idle mixture screw, and the power discrepancy are material differences from the certified design. Importation of uncertified engines is prohibited by Section 203(a) of the Clean Air Act and 40 C.F.R. � 90.1003(a).