I just purchase a used wr450f that came with an FMF Powercore and JD jets.  The bike is as powerful as I would want in a bike for my skill level.  My question is this; if I put the stock exhause back on will I have to rejet?  My issue with the pipe now is the noise.  I plan on riding the bike on the street around town and it just makes too much of a racket.

I do not mind a power decrease....(I know tar and feather me now)...
I do mind the bike running too rich or too lean and then the negative effects of either of these.

Any help would be appreciated.

Thanks,
New and happy wr owner...

firejosh, on 18 August 2012 - 07:15 PM, said:

You can't really put the stock exhaust back on, if you don't want it to over heat, stall, and generally run poorly.
You CAN re-pack the silencer on the FMF, or , put a YAMAHA GYT replacement  end on the stock exhaust can, which will keep it reasonably quiet, and quieter than the FMF.
Then you shouldn't have to change the jetting.