[Bob In Ct]

CO emissions (carbon dioxide) are a result of incomplete combustion and/or a rich mixture. By definition a rich mixture is not providing enough oxygen for complete combustion. Sometimes just adding a PCV valve will help.

HC emissions (hydro carbons) are due mainly to the fact that the wedge engines we all are running have the intake and exhaust valve right next to each other. Depending on the cam, these guys are open at the same time for a lesser or greater period. While they are both open part of the input charge simply goes right out the exhaust valve without ever taking part in a power stroke. The greater the overlap the greater the HC emissions. Cats are designed to burn these unburned hydro-carbons.

Bob