Fitted screamin eagle slash down 06 mufflers to my 07 fxstc with a little cutting around. My local HD dealer informs me I need no fuelling mods, the bike runs fine, no popping or apparent lean areas. Sounds fine like it should, but could I doin damage and not be aware. Gazzer uk.

 

If you haven't done anything to the AC its unlikely to give you trouble.
Its only when you let more air IN that things change drasticly.

 

I have Cycle Shack slip ons and did no fule management or AC mods and mine runs like a champ.Id check your plugs ever once in awhile to make sure it doesnt run too lean. Othere than that enjoy!

 

closed loop systems like on the new harleys do have the ability to adapt to a certain point before the check engine lite comes on. If it doesn't pop on decel and the lite stays off you should be good to go. Good luck on your new ride.