I was told many years ago by Darryl Uprichard of Racetorations that they set all their floats to 5mm. ( This must only apply to the brass type. )
I did this with my triples and it made a critical difference.
Later I got a clear gauge to measure the fuel depth from the top of the well ( where the main tube screws in - remove to check ). I found that 5mm with 3-ring vintage Italian 40DCOE-18s this gives 27mm depth. Oddly, older 40DCOE-18s with brass shafts on another engine gives 27mm with a setting of 8mm. Such depth is the key to when the main systems enters the game, the higher the