I searched around, but the only thread I found close to this would have been a 2+ year old necro thread, so I didn't want to bring it back from the dead. I just installed a Yosh RS-4 pipe (slip-on) on my 2010 YZ450F, and I love the difference it made! It's almost like getting a new bike all over again. I have noticed a bit of difference in how it runs, and though very slight, it is noticeable. With aftermarket pipes and fuel injection (this is my first EFI bike) should I need to adjust my maps? It seems like I need to lean it out almost on the bottom because I am getting a slight hesitation with hard acceleration from down low. Anyone else have experience in this area?