What is the idle on your 580 XLT? What is the throttle plunger hight? What drill bit size will work for this? I dont have the large carbs, i think they are just normal?

I think my owners manuals says 1500rpms

thanks, but what hight does the carb plunger have to be?

Not sure about that, wish i could help ya

Just turn the idle screw on each carb in equally until the idle is correct. 1500 is too low IMO, go with 18-2000.

The owners manual states 1800 +or-200 RPM

make sure that your carb is set to the middle of the five notches on your needle, set your air screw to 1 turn, make sure all plungers sit at the same height, then make sure all of your plungers lift at exactly the same time ( do this by putting a finger in each carb and slightly touch the throttle, once thats done on the under side of your hood it tells you your idle rpm range, adjust your idle screw on each carb up or down equally and you're all set