You will need an FMF 1 1/8 inch powercore/Q4 insert (slimmer one) and your Q4 insert that came with the Q4 (this will also work with a Powercore 4)

 

Note how much smaller the 1 1/8 inch orifice is

 

Get some 3mm short allen bolts and file the heads down a little

 

Next, drill and tap 6 holes in the quiet core (3mm tap) - make sure the threads match your bolts exactly

 

Then I sprayed a little primer on the bolts to keep them from rusting too quickly and tested the threads out

 

and the finished product
YouTube - FMF Q4 with Quiet Core Insert on 2010 Kawasaki KLX250s

 

Nice job! Thanks.

 

Thanks you cant really appreciate the sound difference in the vid because of the sound echoing off the walls, but I took her out for a late night spin.. quiet just like stock but no performance hit.. just quiet performance.. Im so happy now just wanted to share this trick with everyone here.. peace

 

I may try some trickery on mine before the q core comes. The Q on my klx4 is not really loud until you wack the throttle, then it gets a little blatty. My brother has a drz4s with stock muffler and E-header. I'd like mine to be as quiet. Anyway, it looks like I can neck down the tip inside the can and leave the arrestor and baffles alone.

 

Professional job!

I like quiet

David