Could be a few things causing this issue. If I remember correctly the XL has dual carbs........correct? From the description you state, my first impression would be that the idle jet(s) in each carb is plugged. Has the bike been siting without being ran very long? Are you just getting it out from winter storage? These jets have super small passages and can get plugged easy especially with todays gas with so much ethanol which turns to syrup after sitting to long. You may have to do carb jobs on it, which will include the removal of the carbs, taking them all apart, soaking, replacing o-rings, and cleaning all of these parts. If it has been running currently like you state, you may be able to just add some Sea-Foam(can get it at any auto parts store)and adding some to the gas and trying to run it through the carbs as the bike is running. I have seen this product do some crazy amazing shit by just doing this and saving much time and headache. It is of course the cheapest and first option I would try myself. If that doesnt cure your issue than I would proceed into removing the carbs and cleaning them this way. Other things causing this issue could be a lack of compression in the cylinder which will require a compression tester. You are welcome to DM me if you have any questions. Good luck.
