An experimental–analytical investigation on the emissive behavior of two high-performance motorcycles belonging to the most recent European legislative category was being performed by the Department of Industrial Engineering of the University of Naples Federico II. The study was focused on these vehicles because the pertinent information was not very exhaustive in the scientific literature, with particular reference to the assessment of cold-start extra emissions of this particular two-wheeler vehicular class (Euro-3 legislative category and displacement >750 cm3), that is playing a rising central role in private mobility, also in urban context. From this motivation, in this study a calculation procedure was designed and optimized to model the cold-start transient behavior of motorcycles; through this methodology, it is possible to evaluate the cold transient duration, the emitted quantities during the cold phase and the relevant time-dependence function. The whole procedure was applied on the carbon monoxide and unburned hydrocarbon exhaust cold extra emissions of the selected motorcycles, which were measured on the chassis dynamometer. Experimental tests were performed in cold and hot operating conditions, during both driving cycle regulated by law and real-world driving cycles.