Four stroke karting, also referred to as "leisure karting", is there to bridge the gap between league racing, where drivers participate in karts they rent, and two stroke karting, which is very professional. 

The F400 series is a budget conscious formula that are really growing at the moment. Leisure karting is enormously popular in Europe and in the USA. Honda engines are primarily used in most of the events. The 390cc being the most popular.