A very vague question!!! hehe

Depends on a number of things, there is no honest answer....

Depends on CC of the engine, desired engine speed, Cam lift and duration, valve size etc....Truth is u can just play with choke size, remember too small a set of chokes are not always better, smaller chokes increase the speed of airflow and if the opening (Inletmanifold ID) is too great you can suffer from fuel droplet drop out, when the Fuel drops out of the Stoiometric (is that how u spell it?) mixture causing your car to run lean... again Larger chokes might not allow the airspeed to be high enough to achieve proper atomisation....

The best way is to play about, start with what u have and try it, I changed my chokes down 1mm in my dellortos, i saw no power difference that i could tell and they skinned me 80 quid for the chokes!!!

Iain