At 120, you'll never get it "right" at any setting. The best you can do is turn your your compression, rebound, and preload all the way down and make adjustments from there. The shocks are valved and sprung for alot heavier rider so us "lite" people(I'm 140) can't really get the most benefit from the shocks.
Derisi Racing and TCS(and possibly other shock companies) can rebuild your stock shocks and make them way more compatiable for your weight and riding style. http://www.derisiracing.com/atv/atvindex.htm
A forum community dedicated to Yamaha YFZ owners and enthusiasts. Come join the discussion about performance, modifications, troubleshooting, maintenance, classifieds, and more!