Rust, make sure there is no rust. see how much play the chain has (move it up and down) there should not be a lot. if there is you can usually tighten it, but if it is stock gearing you may (for performance reasons) want to change them both (front, and rear) out. A lot of people here change sprockets. I have vortex ones on mine.

 

make sure all the teeth r on sproket chain isnt rusted or crackin make sure it has oil on it and check the dip stick or the window which ever it has stand it straight up when u do that so its level,and check the fork seals make sure theres no liquid comin out and its clean and not to sure on this but make sure theres no water comin outa tha exhaust,and if the brakes suck and it shakes check the rotors for warping