NISSAN Pickup 86 Motor Z24

K such !! I have a couple of doubts regarding the fuel performance of my Nissan, I hope someone can help me and if it is possible to give a recommendation.
The detail is that gasoline spending for me is a lot taking into account that it is a 4 -cylsome engine.
Does anyone know how many kilometers per liter should this engine give?

And the other is: how does the fact that they have made the modification of the original system by a carburetor affect the performance?

Note: It is a Ford 302 carburetor

if someone can handle me with this please, thanks in advance !!!