On carbs which have float chambers, such as webers, the float chamber has a vent on it which equalises the air pessure in the float chamber with the ambient air pressure. If you want to use forced induction, ie turbo charger, by using this port to pressurise the float chamber with the inlet charge (including it within the inlet tract), the fuel pressure will inrease at the same rate as the inlet pressure, thus increases fuel flow through the jets keeping the air fuel mixture in proportion.
Like the others said a rising rate regultor is used (just like on injection) and an electric fuel pump.
On the old TVR 3000M they used a normal carb and mounted it in a cast iron box which was pressurised, the fuel pump had a hard time of it.
The solex as found on ph2 ren 5's, 11's, 18's and Fuegos is basically the same as a normal solex 32 BIS but it has a magnesium upper body, re-inforced float chamber gasket, the throttle shafts have lip seals, accela nd power valve diagphrams are re-inforced, idle jet has a plug and seal and the gasket face is larger. This is done so the boost doesn't leak out and blow things apart.
I think my dark dirty little secrets out now, I am a renault man!