This is how one of the the pump jet seat for the ball inside looks like. It has a spiraling cut which makes it impossible for the ball to seat right and close the pump circuit. The vacuum in the carbs was thus pulling gasoline through the pump jet. Some ball seats looked better, but I drilled on all of them a conical seat for the 3mm ball to fit right.
The result has been that the webers do not dump gasoline any more into the throats when resting and absorbing the heat from the engine.
So that one problem seems to be taken care off.