You are running too rich with your carburetor - check to make sure your float level is not too high or that your idle mixture screw is not backed out too far. Jets might also be too big. Some carburetors need a vent to manifold vacuum through the base and in many cases the gasket is not properly cut to provide that vent.
Bottom line - too much fuel and it is going to take some sleuthing to figure it out at the carb.
