I had a similar problem with my Besson when it was new (back around 2008ish.) For probably the first 3-4 years that I owned that horn, the 2nd valve...
My understanding from the USA importer back when I was a Besson Artist is that the curved/adjustable bell design was more or less an experiment meant...
I'm curious as to how this horn plays relative to the fixed-bell Besson 181/New Standard/767 instruments. I once owned a Besson 3-valve compensating...