For those who are resurrecting bikes from the ashes the throttle twistgrip sometimes gets overlooked. You can loosen the screws some and slide the twistgrip throttle tube part off the handlebar. You may find rust underneath so you then clean the bar end it rides on with a Scotchbrite or whatever to clean metal. Bikes with painted bars may take some sanding with emery cloth. Apply some grease where twistgrip rides, but not in clamping area, and reassemble. It can make a big difference in a light easy throttle pull with no binding etc.
