Mechanical condition being good, response problems are going to be carburetion.

Under hard decelleration (sic) most carbureted engines run extremely rich (engines modified to reduce emissions do this to a lesser degree). If 'slowing down fast' tends to stall your machine, it may be getting too rich to run.

Make sure your idle and pilot circuits are set correctly. ..and clean your air filter about twice as often as you think you should!!