I put V&H Monster Rounds slip on mufflers on my 2002 flhtcui and was wondering if I need to put a fuelpak and high flow air breather to compensate for the change of mufflers?

 

Should be no issues as long as you don't put the high flow air breather on. Your bike will however, I found ran better with the FuelPak fuel management system even without the high flow air breather. You will need some kind of fuel management system if you add the high flow breather. Added benefit is you get some extra torque and an a few extra ponies, as well as the bike should run a bit cooler. You may also notice the throttle is a more responsive with the Fuel Pak.

 

Put a fuelpak on my wife's street glide after changing only the exhaust. Swapped stock to Vance and Hines Big Shot Duals. Definite improvement without changing the air cleaner. Don't know that it was necessary, but the big shots are an open system (no catalytic converter) and so needed a little cleaning up if ya get what I'm saying (fine tuning). Even called V&H and they gave me a couple of adjustments that didn't show up on the map off the internet after I told them what the issue was. May very well be fine with just slip-ons, although I think the cats were in the mufflers back then. Now AFTER we installed a stage 1 air cleaner, talk about waking the bike up. WOW. In response to your question, NO, not necessary. But as Nute said above, it does a make a difference. They run these things so lean from the factory.

P.S. If ya watch the touring parts section often on this forum, you might get lucky and pick one up on the cheap. That's where we got hers.