the size of carb, and the intake configuration depend on what you expect the engine to do. If you want low end torque, and snap off the line, then you are over carbed. If you are looking for a high revving engine you are in the ball park.

The easiest way to explain this is to start by establishing that air moves through the intake as a liquid. By making the venturis in the carbs smaller, you increase velosity. This increase of velosity flowing through a dual plane intake is what is needed for efficient torque. The idea here is that the air will gain so much momentum that when the piston reaches bottom, the air flowing through the carb will flow all to the way into the cylinder, and thus start compression before the valve closes.

A larger carb, and a single plane intake work best at higher RPM ranges. At higher RPMs the engine is moving so mush air, that a smaller carb just makes resistance

When you understand velosity, carbs will be much easier to tune. When the velosity is greater (smaller venturis), the air flowing through the carb increases the low pressure in the jets, and more fuel is drawn through. When the velosity is slower (larger carb) the carb drafts less fuel. This is why an engine leans out when the carb is too large (engines often backfire in the intake when they are too lean) A larger accelerator pump can help, as well as changing jets. When a carb is too big you have to go with larger jets because there is not enough of a low pressure area created to draw the gas through the smaller jet, This will cover the problem, but you still lose some of the low end torque

I hope this helps. This is over simplified, and is just the tip of the iceberg, but to go into this subject in depth could take hours and many pages