In this video tutorial, viewers learn how to tune a HPI 21BB engine. From the base settings, start adjusting the high speed needle in a 1/8 turn. Then adjust the low speed needle in a 1/8 turn as well. Make sure to never run the engine too lean because this can damage the engine. The mid-range needle does not need to be adjusted, but make sure to always run it on base settings. This video will benefit hose viewers who are interested in auto mechanic or have this engine for a vehicle, and would like to learn how to tune it for proper use and efficiency.