Fast Idle RT100

I just purchased an RT100 that had the top end rebuilt and a new carb installed. It starts on the first kick with the choke on and idles high as expected. The RPMs come down as it warms up. As soon as the choke is off, the RPMs go sky high. I can bring it down to a normal idle by moving the idle screw a bit or putting it into gear and moving forward a bit. When I put it back into neutral the RPMs are normal, however the throttle response is sluggish and feels as though its bogging down somewhat. Any suggestions on how to tackle this problem? I've tried to make a few small adjustments to the carb but the result is still the same.