your 488 has 2 idle screws. One for each carb. The newer liberty motors 2001 and up have rack style carbs which only have the 1 idle screw for both carbs...
You need to start the engine, and turn the screws evenly counter clockwise until the idle is 1800-2000. I mean slowly, and evenly. And give your throttle a flip everytime you loosen the screws. The main thing is to get them even. If its not a big chore, take the air box off. (Most airbox's are no easy job though) Look in the throat of the carb and see if the slides are pulling up at the same time. If they aren't, you'll need to set them and thats another 10 post thread...
540 Open Mod
1995 Polaris Indy 500
White EPI primary spring with 10 weights
Purple EPI secondary spring, 45/36 HRP helix