Mikuni HSR smoothbore carburetors give superb throttle response, and deliver all the airflow needed for any level of Harley performance. Being one of the best upgrades you can give your motorcycle, these Mikuni carburetors substantially increase power compared to stock. However, it is the dramatic improvement in throttle response that makes these flatslide HSR models such outstanding performers. Mikuni HSR 42mm and 45mm smoothbore carburetors are offered individually to meet the specific custom application needs of performance engine builders. They are available in standard or polished aluminum versions.