You will need an 8mm socket, 3mm hex key and a SAE 7/16" wrench for this task:
Using the metric tools, remove the nut and washers on the throttle return spring bolt located on the throttle arm. See Arrow 1 below;
Guide the spring from the bolt and then unhook at Arrow 2;
Loosen the hexnut at Arrow 3 with the SAE tool and then turn the anchor clockwise to decrease its height. Tighten hexnut and preserve the orientation of the anchor so it is as we ship it;
Rehook the spring in the same manner as shown in the photo below;
Secure the spring to the bolt at Arrow 1 and attach washers and nut as stated in #1 above - you will require effort to respring it as the increased tension needs some elbow grease. Make sure the spring is on the silver part of the bolt AND NOT the threads.