This year I need to do it.
St. Francis was famous for observing the fast in preparation for Michaelmas or the feast of St. Michael, September 29. During the lent, on September 17, Francis received the stigmata at the solitude on Mt. Alvernia. I think the Franciscans once observed the lent, as was the custom for the devout during medieval times - not sure if it is done today.
The lent begins today, the feast of the Assumption. It seems appropriate to observe it this centenary year of Fatima, especially since it is believed St. Michael was the angel who appeared to prepare the children for Our Lady's apparitions, and was the angel with the sword in the vision of the secret.