Jet Needle for Rotax Max Kart Engines. Denoted by item (3) on the diagram, this needle is an adjustable fuel metering component that attaches to the Rotax throttle slide for all Rotax Max Evo kart engines.
With various 'clip' positions for the fuel metering available, the jet needle is a vital tool to properly adjust the fuel and air mixture from partial to open throttle, and moving the associated circlip up or down on the needle can help adjust response off of the corner to mid range on throttle.
Generally, a de-tuned Rotax category such as Micro or Mini Max may utilize a 'lower' needle position, while higher up may be for engines that can readily in take more air vs. fuel.
Replacing the needle in your carburetor is a routine service item if you suspect your needle has been bent, chipped, or warped.