I always thought that the best way to manage a 2 stroke was to keep it running. It probably is not running when going down hill and using the engine for braking. There is less heat and a good amount of residual oil during a downhill run so the engine generally survives. That said I believe that the load on the bearings are just as high downhill as when running, so lubrication is still an issue. I suggest trying to keep it lubricated with throttle blips and good management. I am not a fan of improper jetting, expecially if it is WAY too rich.
Chris