Is it wrong to change the carburetor for peugeot 405 for a carburetor of peugeot 404 or 504 would the consumption go down?

my experience is that the original 405 carburetor when functioning well is more economical than fitting a 504 or a 404 carb.

the whole 405 carb unit must be functioning well for it to offer good fuel consumption. with it i manage 30mpg in city drive and up to 39mpg highway. the 504 and 404 carbs cannot achieve that, the best they can do is a max of 35 mpg given that the engine and the car in general is functioning well.