Carburetors designed for 4 stroke engines are designed around a basic principle. At lower RPM's, the fluctuations in velocity are great. Think about it, a 4 stroke only intakes air half as often as a 2 stroke. When the intake valve opens and air begins to rush into the cylinder, the pressure inside the carb drops VERY fast but the flow is still moving relatively slow. Because carburetors are designed to work off vacuum induced by flow (see Bernoulli's principle), they're designed NOT to function with engine vacuum. In fact, they're designed to work with engine vacuum to regulate flow speed at lower throttle settings to nullify the effects of engine vacuum on the fuel pickup rate. That's why most have a butterfly and then a vacuum controlled slide. If you watch the slide as the engine comes off idle, it bounces up and down.
2 strokes have a shorter intake tract and need fuel and air twice as often. They need a simpler and more direct fuel supply.