This problem comes up on this board about once every year or two. Have you checked the archives?
As long as no other problems like outside air getting past the carb. throttle shaft (Worn?) or in the manifold somehow,(Crack or gasket leak?) And if you have a good working governor assembly, your problem probably is the link between the governor and the carb.
I don't know how to set it up so it idles and is also very responsive, but there may be instructions in the archives.