1) From Mark Huggett
"Adjustment of the tab is done at the Bing factory and I believe
that it is described in Haynes or other workshop manuals.
What is important to know is that these carbs are not fuel tight when the
fuel tap is open. That is, you have to close the fuel tap every time when
the motor is not running. Most pre 1969 BMW riders, including myself
usually turn off the tap 50 to 100 meters before home so as to empty the
float bowls."
2) From Bing Agency, KS
"The wrong jet sizes will not make it overflow.
The correct method to lower the fuel level is to bend the brass lever.
With the levertop turned upside down, so the lever is resting on the float
needle, measure up from the rim of the lever top, where the gasket is. The
factory measurement is 22mm. This is very close to overflow. I usually
make the distance 22.5mm."
So I guess this sums it up pretty well
Pierre