thanks guys. now. I'm not trying to build a race bike and don't want to do allot of mods so i think i will go with the 30mm. or i should ask how big can i get away with and not cause the need for more mods?
Mikuni doesn't make a 30mm flatslide. Those are Taiwan or Mainland China Keihin "D" slide clones. You'll be happier with the genuine Mikuni when you need floats or gaskets.
I didn't say it was a Mikuni, just a clone, and parts are available on the net.