Yamaha xs400 carbs leaking fuel

After a full rebuild, the carbs continue to leak fuel at the rear through the jets, does anyone have an idea how to fix this.
The floats are not broken. When I test the float needle by moving them up they seal very well. When the floats are set to close the float chamber with the least amount of fuel, the problem remains and the fuel just flows through.
I hope someone has experience with this and can advise me