I would want bought UFO's but I heard that some persons had difficulty adjusting them in the forum. I have an EXT 580 1994 carb I would like to know what is the good setting of jetting.

They change your jetting quite a bit. The EXT has 38mm carbs, so the bennefits of the UFO's will be less, but I did find an improvement in midrange throttle response and power in my 94 ZR580. I went way down on the pilot jets and up two sizes on the main jets. I also have 3.5 cut away slides.

ok, just for fun, what is it your stock jetting and what is the present jetting??

Pre UFO - pilot jet #35, needle clip position 5, main jet 330.
Post UFO - Pilot Jet #10, needle clip position 5, main jet 350.
With Tempa-Flow (current setting) - same as post UFO except 360 main jet
All these are with 3.5 cut-away slides. My needle jets are obviously not the original pieces, but I do not know what needle jets I have.