These main 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 main jet affects fuel flow to the engine the most at full throttle but has some affect at part throttle. The closer the throttle is to full, the more influence the main jet has on fuel flow. A larger size increases flow. A smaller size decreases flow.