I rebuilt my 1990 last winter and added the same pipe and silencer. I also had Fredette do some porting work and he told me that if I was close before, I would be close after as far as jetting is concerned. The reasoning was that I had improved both the intake side and the exhaust side. I would think you'll probably need to dial it in a little to be optimum. I think I need to spend some time jetting my bike but it seems like I'm spending all my work time trying to dial in my boy's YZ80. When I have time to ride, I just go and figure I'll optimize the jetting "next week".