I believe that year RM was set at 3/4 or 1 turn. The setting is from when the spring is in it's neutral state. Remove the adjuster knob and, with out moving the spring, replace the tang of the spring into the back of the adjuster. The position where the adjuster ends up is your start point.
Turning it clockwise will increase the tension
If the motor tends to bog when you open it up, back off on the spring tension. If you seem to loose your low end power too soon, increase the spring tension. You'll have to play with it to get the best low and top end power. The spring tension will only change when the power band kicks in. It can smooth out the transition from low to high and reduce the "hit"