The partnership of Vittorio Minarelli and Franco Morini was the basis for the most successful two-stroke motorcycle engine production company of the postwar era.
In 1952 they introduced the Gabbiano 125cc two-stroke with the horizontal engine slung beneath a low-slung single tube frame frame. This was followed by the Vampire 200cc and in 1955 FBM began producing engines for other manufacturers.
Towards the end of 1956 the partners had a falling out, and separated. Minarelli formed FB Minarelli, and Morini moved to Zola Predosa and created Morini Franco Motori in 1957.
Both companies built small-displacement two-stroke engines, and each achieved considerable success.
There appears to be no relationship with the Gabbiano firm of Florence which was established around the same time, apparently, but are best known for their off-road machines in the 1980s.
Another Italian marque named FBM built speedway machines: FBM Speedway
Sources: MC Storico Conti, Henshaw et al