Bike came with an hmf exhaust on it. It has the quiet core installed but is still much louder than what I would like. Anyone ever attempt modifying the quiet core a bit? I was thinking of welding up the inlet of the core and drilling a series of holes in the sides instead. I don't imagine it will hurt the performance too much, but should take some of the rasp out of the exhaust.

 

Yes, those HMF pipes are loud. I had one for a while and thought of doing what you're thinking. I noticed that turning the quiet core around so that it stuck out was a little quieter, but looked silly. I ultimately sold the HMF to another member here and picked up a FMF.

 

My FMF PC4 was very loud and I couldn't seem to source a quietcore insert (were backordered for 3 months), so I just made my own insert out of sheet metal. I made a 'tube' with the sheet metal that was just small enough to go into the end of the muffler, then bent over the front of the tube (by cutting about 10 short cuts into the tube) so it was more cone shaped at the front (part going into the muffler). I then drilled a hole in the tube to line up with the mounting hole in the muffler that the Quietcore insert uses. With this setup, I can adjust the volume somewhat by taking out the insert, and bending the cone a little more so the inlet hole is smaller or larger. I then did the same for my 2009 KLX250s as well. I don't have any pics - they'd probably explain it better, but I can get some or draw something if anybody needs more info.

 

Did you have to make any adjustments to your jetting? Usually, less noise = more resistance = richer air/fuel mixture = leaner jetting required.

 

I have a standard Dynojet jet kit in it, 128, 3rd notch on the needle, with the snorkel removed. I really didn't notice any difference in power (although in reality the difference is likely too small to notice without an actual dyno run) between the FMF with no silencer and my home made one.