WR jetting questions aftermarket exhaust installed

I have ordered a 2004 WR450 and I would like to add a FMF 14" exhaust to the bike when it arrives. When I change out the stock exhaust should rejet the bike. If so how long after break in can I make the change, and what do I change it to.

I put on the FMF Powercore and changed the main jet to a 165 from the stock 155. The pipe gave the bike a great bottom end but the jetting still seemed off on top even with the 165 main. There was a hesitation between half and full throttle. I then ordered the James Dean Kit and put in the Blue needle on the midlle clip and installed the 168 main jet. Now the bike rips from bottom to top at any throttle opening. (The kit reccomends running a 170 main but I went one size lower since i run the quiet core insert once in a whaile and the 170 was too rich with the pipe plugged up).

For your second question, I dont think you need to wait to break in your bike in order to jet it properly or put on an aftermarket exhaust. I would set it up the way I want it right away.


Order the JD jetting kit off of this web site! It works with all pipes for the WR450. Worth every penny. :)

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