The effectiveness of using catalytic aftertreatment to control excessive hydrocarbon and carbon monoxide emissions is well known. However, a thorough understanding of how the catalyst and vehicle work together as an integrated system is still in developmental stages. A major goal of the investigation was to examine catalyst performance under the dynamic conditions existing during normal vehicle operation. The impact of applying catalytic aftertreatment, with and without the addition of secondary air, to three small 2-stroke motorcycles is examined. It is found that catalysts respond well to the varied conditions encountered with 2-stroke engine powered vehicles. While the addition of secondary air is beneficial to increased hydrocarbon reductions, its impact on carbon monoxide can be variable and a function of vehicle operation.