Delnari - Where are you in Japan? I see you have the Rough and Road site up there. I am here in Japan also. I am military in Yokosuka. I ride a 2005 DRZ400SM. PM me here and we will talk.
Bill1960 - I have the Yoshimura carb on my bike mentioned above. It is awesome, huh? It was expensive, but so worth it. At first I had tuning trouble also, but Yoshimura helped me work out the bugs. Check this site: http://www.yoshimura-jp.com/en/index.html It is Yoshimura Japan but English version. Yoshimura has many English speakers, and you can mail them. They are more than happy to help in any way. I can vouch for that. I can also call them for you if you can get a parts list to me. All is up to you, but I gave you a starting point. I hope it helps.