There is a less expensive alternative to replacing the stock fuel valve with another stock valve. Non-vacuum valves are available from sources like Bikers Choice for under $15. Combined with a Pingle adapter plate you can have a valve with on-off-reserve for under $30 including shipping. Here is a link to the Yamaha 650 site that goes through installing a valve. Pingle makes an adapter plate that has pre-drilled bolt holes for different metric applications. If you want to keep the vacuum function you can buy Harley style valves that are vacuum operated.
http://www.650motorcycles.com/Petcock.html If the link doesn't work (because of the word "petc0ck" try typing the following in your browser:
http://www.650motorcycles.com/Petcock.html and substitute the correct work for Petthingy.
I tried to edit it to allow a link to function and it worked on preview but not in actual use. Bleh!
Rob (Savage_Rob)