I believe it is vacuum assisted - so I guess the greater vacuum created when the throttle is closed is used to take some of the tension out of the clutch springs allowing the clutch to slip if the speed differences between the drive and driven plates are too great or too much torque. Was this the type of thing fitted to the later TL1000s “Widow makers” To stop the “born again bikers" killing themselves locking up the back wheel when entering bends?