After swaping rides between a friends 400 and mine I noticed the suspension wasn't set as soft as his. He also noticed how stiff mine was, How do I go about setting it softer? The front shocks seem fine. We both way about the same (200lbs)

 

If you are referring to a 400EX then I assume you already have the compression adjustment **** located on the shock backed off to the "soft" setting. This only makes minor adjustments and you will not notice a big difference. The next step will be to back off the preload on the spring of the rear shock. You do this by loosening the the jam nut and then the big nut on top of the spring. By reducing the tension on the spring the suspension will become softer. This can be done with normal wrenches, but is much easier using a spanner wrench designed to adjust the shock spring.