Welcome to OTT.
Wish I had the time to search for you right now, but there are several threads regarding this issue on OTT.
Most, as I remember, are about BX series tractors but some are related to B's also. As I recall, most are about the detents at the height-adjusting knob itself..... the deck will "click" itself down as I recall.
Maybe try the "Search" function at the top of the page for "mower height" or similar....
