This high flow air filter fits in the stock air filter box. UNI makes the highest quality air filters that flow many times better than stock air filters. With this additional air entering the combustion chamber you will need to add more fuel as well. Drill the main jet with a #72 drill bit (.025") for the additional fuel. The bigger air/fuel charge will create more power in your 49cc motor. See our how-to section for more details on this product.