Well there are 4 different sizes of float valves foe DCOE Webers, 150, 175, 200, and 300, so presumably, like the main jets, that equates to 1.5mm, 1.75mm etc.
QED tell me that a 1558 TC pushing out only 125bhp requires a 175 needle valve.
They told me that a standard mechanical fuel pump has been known to pump at too high pressure (3.5psi seems to be the limit) , so if new float chamber valves don't cure the flooding, my next thing to do would be to fit a fuel pressure limiter on the output from the fuel pump set to 3.5psi.