In cold weather conditions, starting and maintaining low speed stability (engine idle RPM) has been difficult for smaller volume (50cc to 200cc) single cylinder engines. In order to improve the cold start ability without causing any inconvenience to user, automatic choke systems (auto-choke) have been employed. These auto-choke systems enrich the fuel-air mixture depending on predefined operating conditions. For Euro III and Bharat Stage IV (India) emission legislations, cold start emissions are very critical. The objective of this study is to investigate the effect of auto-choke systems on CO, HC, NOx and CO2 emissions in addition to studying temperature and light-off characteristics of catalytic converter of a 4-stroke scooter engine. The vehicle was tested on chassis dynamometer to investigate emissions on WMTC and ECE R40 test driving cycles, with and without the auto-choke system. Three durations of auto-choke operations were studied. The experiment was done with and without after treatment devices (catalytic converter and secondary air injection) to understand the engine out emission characteristics. One of the observations was enrichment of fuel-air mixture due to automatic choke operation results in significant early light-off of the catalytic convertor.