Well, On the 250F with a vortip it ran weird until I went lean on the jetting especially the mid (needle) and the main. I ended up rich on the pilot. Then it ran like a raped ape. I think if you play with the jetting you'll get it to run the same. I feel now I lost nothing in power compared to the stock open exhaust. Jetting is everything you just have to adjust it until you get it right, no matter what exhaust or air combo your running.