First, when the engine starts does the pull-off open the choke blade a little? If not, you need to adjust/replace the pull-off.

If the choke blade is opening, you need to adjust the fast idle; this is done by bending the arm that contacts the fast idle cam. Insert the blade of a common screwdriver in the slot in the red circle below and bend the arm away from the plastic cam. Trial and error will achieve the desired fast idle rpm.