Here is an example of 2 choke discs for Linkert Carburetors.
On the right is Choke Disc 27225-36 which was used on all 1-1/4" and 1-1/2" throat Linkert carburetors up until 1948. In 1948 choke disc 27225-48 on the left, was created to address the common issue of carburetor fires. This spring-loaded disc would be pulled back as the motorcycle started, if then the carburetor backfired the force of the backfire would push the disc closed to cut off air. Without the air the fuel fire would not ignite, and the starting sequence would begin again. Most backfire issues were the cause of either improper timing or incorrect adjustment of the fuel delivery needles.