Enlarging the venturi would be like flattening the airfoil on a wing where you would lose lift by doing so, On the carb you would lose fuel suction by doing so. The venturi is of a very specific shape. If you were to cut a carb in two the venturi would look just like an airfoil. There are so many model #s because, just by changing the throttle arm, for instance, you would need a new number because now that carb will no long fit the motor that the carb number refers to.