Ed
Guest
Had similar problem with my 1688.  Replaced the spring with a new, heavier one. Saw the two side by side - the old one was about 1.5 inches shorter. The problem with the rotor slowing has gone away.  I gather some springs may have been of poorer quality steel - is your dealer using up old stockIJ   Mechanic advised me to make sure to keep the unit greased so the moveable sheave can move.
 