That depends on the carb. If your idle mix screw tapers all the way to a point you will be able to adjust it out a turn or so, to increase the fuel ratio. Others use a mix screw that stays basicly straight, and will end in a short-fine taper. These generally have to be jetted. I run a technigas w/ a delorto carb, and had to go up 3 jet sizes to get an even idle. I use pin drills to open the jets, you can also easily open them w/ welding torch tip cleaners.