Do I need to rejet?

Ok so I ordered a new fmf fatty pipe and shorty silencer for my 2001 rm 125. My old exhaust is a PC platinum and r304 setup which called for a 460 main and a 3rd clip position. Now im assuming this is what my jetting is rite now because the bike has always ran fine and never fowled any plugs, my bike came with the PC setup. However the FMF calls for a 450 main and a 2nd clip position everything else stays the same. I rode the bike yesterday with the new exhaust (FMF) and it ran great the only difference was the new sound. So my question is do I really need to rejet or should I just leave it if its running fine? 

It may be 'running fine' but unless you try stuff you'll never know if more power is yet to be discovered from simply fine tuning it.


Why not experiment a bit with the needle's clip position,

at mid throttle you'll either notice a bog if it's too lean, or stuttering if it's too rich.


For the main jet, use this handy guide :


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