Scott,
The main problem with the Yamaha Lawn Tractors is that they were only made between 1989-1991, and thus parts are getting hard to find, and some are just no longer available. Best thing to look for any lawn tractor is if it has been maintained. Engine, tranny, differential oil changed regularly, etc. There are no carb rebuild kits, but there are individual pieces. With the key in the "on" position, you can turn the PTO switch on, and should hear an audible "click"...that would tell you if it is powering up correctly. Otherwise it may just need to be adjusted, which is covered in an older post on this forum.
Rattosh51
YT6800