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Message: [QUOTE="1998RM250, post: 1388548, member: 99032"] After looking on fmf's website on jetting specs for different bikes, I was wondering why the huge differences in jets? For example my 2001 RM 250 it says a 158 main jet, and for 2002+ it has a 170 on some bikes when those years are all pretty much the same motor. That seems to be a pretty big difference, and i noticed even some of the older RM 250's running a 152 main jet on fmf's site which seems really lean! I was wondering what gives with the jetting, I'm trying to figure this stuff out. :bang: [/QUOTE]