Don't know how may people have done this on the 325/330 and especially Sportsman 500s when they have rebuilt carbs,checking for running problems,etc. Polaris like a lot of manufacturers jets their carbs with consideration for the air box and filters installed and if removed they will run lean and run like crap every time. Glad you finally found the problem. Hope this helps anyone in the future that air boxes and filters have to be on to check for running problems.