This is a very tricky symptom with OS carbs but first of all I suggest you go back to factory settings, specially on the LSN needle, than just work around the HSN needle and the idle screw.

When you run it hard and you come into stop the engine seems to have a very high idle and then starts to drop in increments, it is because you have to much fuel left in chamber and engine has to burn it before idling, so try leaning the HSN needle a little at a time while reducing idle speed opening idle screw. It is very tricky, but just be patient until you find the right balance.

Trust me don't fool aroaund to much with LSN. OS carb is different than Nova and Picco carbs.

AFM