Mike P,
I agree with Steve B. and Jim S. From your problem description, it sounds more like a governor or governor linkage problem rather than a carb problem. First thing I would do is inspect the linkages between the governor and carb throttle connection to make sure everything moves freely and nothing is deformed. Check to make sure the governor spring is in the correct hole on the governor arm. Then I would perform the governor adjustment instructions noted in the Service manual and see if that fixes the problem.