These idler jets fit Bing 54, Bing 64, and Bing 84 carburetors commonly used on Rotax, HKS, Jabiru, and other sport aircraft as well as some motorcycles. The idler jet affects fuel flow to the engine the most at closed throttle but has some affect at part throttle. The closer the throttle is to closed, the more influence the idle jet has on fuel flow. A larger size increases flow. A smaller size decreases flow. These jets have small passages and clogging is a common cause for starting or rough idle operation.