Like SSH said.
1st thing is triple pipes. I'm partial to the Benders. Night and day difference. Then start dropping weight. Due to the age of these, there'll be a pile of cheap used parts around. I never did it, but swapping in a Cat skid is the cheapest and easiest way to drop weight and make it work better in the pow. I don't think Yamaha could have made that skid any heavier if they tried...