I'm new to outboard motoring, I was a day sailor for many years and sailed a 16' boat w/o any utility power. I now have a 25' boat with an old Johnson circa late 80ties. The throttle handle has two movable parts, first obviously the throttle and a rotating knob on the front middle part of the handle. Is this to increase the tension on the throttle? This is a 8HP motor, any one knowledgeable welcomed, thank you.