Why won't my 2002 Yamaha warrior starter engage?

If your starter free spins when you hit the start switch the most likely problem is the starter clutch. http://www.imagessite.com/OEM_Images/Yamaha_atv_images/00YFM350XMB7.gif

Pull the stator cover/assembly off, revealing the flywheel. Behind the flywheel is all of this stuff. You'll need a flywheel puller and this then slides right off. Part 9 is what fails, but can also result in missing teeth on the large gear(part 6) that mates with the starter gear (part 1). You may also want to rough up the raceway on part 6 where the starter clutch rollers engage. NO LUBRICANT HERE