I have a 96 with a mikuni 42 mm and it acts the same way. It is normal and indicates proper idle circuit jetting. My girlfriends xt225, same exact thing. I leave choke on and ride it. Don't let it sit and run, as it will start to run too rich before fully warming up, both bikes the same. I just start it, let in run in choke until it just starts to slow down some, then take off riding and turn choke off when it can hold an idle, bout 2 to 4 min.