I have a 2001 with a Kirker 4 into 1. I don't know any of the history on the bike but my suspicion is that they never rejetted the carbs after they bolted on the pipes. I will do a compression test and check valve lash when I get around to it but just want to ride it for now. It has 27,000 miles on it.. It's not too bad, the pops are not very loud more like a sputter at certain RPMs. Not looking forward to pulling the carbs and messing with them or paying some else to do it with unknown results. If I do find it necessary I'll wait till January when I won't be riding much anyway. Maybe just cleaning the carbs would help but how could I recognize if a jet kit has been previously installed? And what kit would be a match with the Kirker and stock air box? I'm not looking for more power (it has plenty for me already) I just want it to run as good as possible.