Randy, I had Vance & Hines slip-ons put on my bike before picking it up when I bought the bike new. The dealer told me that re-jetting was necessicary so I had them do it when the pipes were put on. I sure do hope they were telling me the truth, I´ve since read conflicting remarks, but either way, mine was re-jetted!!! You may do well to contact either Yamaha or V&H to get their feedback??