FMF Q4 Repack with sound data

I figured it was about time to check the packing on the FMF Q4 on my 2008 WR250x. I purchased the bike with about 2800 miles on it, the Q4 was already installed by the previous owner. The bike now has 10240 miles. I don't know exactly how many miles the bike had with the Q4, but at least 7500 miles or so.

I figured I would try to get some sound level data before and after. I also had a spark arrestor insert from the previous owner that I installed that seemed to make it quieter, so I thought I would see how much with some objective numbers.

I tried to use the SAE J2825 static sound test that the AMA has been pushing. Basically, you put the bike in an open area (at least 8 feet clearance all around), run it at idle, hold a mic 20" back from the outlet of the pipe at a 45 degree angle. This is to be repeated at 2000 rpm for any bike with less than 4 cylinders. Well, 2k rpm is like just above idle for the WR, so it really made no difference.

I tried using a sound meter app for my phone (Samsung Galaxy SIII) but unfortunately the hardware limitation of the crappy mic is only 84 dB. But I read somewhere to try blocking off the mic port and adding 30 dB to the calibration of the meter. So that is what I did. Which means the numbers here are only RELATIVE, and I would not rely on them as absolute or accurate values.

Anywhoo, before I changed the packing, with the spark insert, I was getting 91 to 92 dB at idle. When I removed the insert, I was reading about 96 dB at idle. So that confirms that the insert does objectively make it quieter (at idle). Subjectively, it seems to reduce the deep rumble and bark when the throttle is open.

Pipe with the spark arrestor insert (The insert is FMF model S9000)

The insert looks like this and has a screen inside:


So I pulled the pipe, opened the can, and found this mess inside. The packing also felt very damp, but didn't smell too much like fuel or anything.



[Wow, those are some out of focus pics. Guess I was in a hurry.]

That explains why the inner sticker on the can peeled off a few months ago. There was basically no packing left on the inside in the back. I did some research as to the right stuff to get to repack the can, but I think I got the wrong stuff. FMF website lists two different kinds for four stroke, the regular and the performance. I tried to get the performance one, which is supposed to be red? Here is what the bag said, FMF #11393.


But it wasn't red, and it was a real pain to work with. It was just a bag of random chopped fibers.
Clean inner pipe:


After I tried to wrangle the random mess onto the pipe:


It took several attempts and much more tape to finally get it all tight and into the can. But I got it back together and rechecked the sound numbers. With the new packing, it was now 89 to 90 dB with the spark arrestor insert and 92 to 93 without it (at idle). So this says that objectively the new packing reduced the sound at idle.

But... subjectively, I rode to work this morning with the spark arrestor in place and on hard acceleration and mid throttle, it either doesn't sound any different at all or maybe a little louder. Also, initially the bike stalled a few times and was very 'poppy' until it warmed up. Maybe it was just the packing getting broken in and the tape burning off. Maybe I need to adjust my fuel programmer now that there is new packing in place. I also didn't really notice any performance difference subjectively. But from the condition of the old packing, it needed to be done. Next time I will buy different packing. They sell a pillow type that looks much easier to work with.

Looks very familiar:

https://wr250rforum.forumotion.com/t8979-fmf-q4-exhaust-repack-melted-coupling-spacer?highlight=repack

motokid wrote:

Looks very familiar:

https://wr250rforum.forumotion.com/t8979-fmf-q4-exhaust-repack-melted-coupling-spacer?highlight=repack

Wow, almost exactly the same. I think I ordered it from Amazon, but now I know that part number is not the right one to get. I will make sure it is the pillow type!

BTW, your inner pipe looks slightly different than mine. That secondary layer of mesh over the end of the perforated section is different. Mine is a bit shorter and looks like a tighter mesh screen, while yours looks more like chain mail.

Also, I have an FMF header (powerbomb) and my commute to work is about 40 minutes, so it definitely reaches full temp on a regular basis.

Did you notice any noise reduction or performance increase after the repack?

dmmcd wrote:

Did you notice any noise reduction or performance increase after the repack?

Nope.

motokid wrote:

dmmcd wrote:

Did you notice any noise reduction or performance increase after the repack?

Nope.

This is why I haven't bothered to repack mine. Anyone think it was worth it?

I repacked my FMF PC4 once and it was an absolute bear to get apart but maybe that was just mine. It only had a small hole of burn out so not really needed. Still super loud.

That said, I'm really not impressed with FMF. I also had a powerbomb header and it had a habit of burning through expensive riding pants. So I got an FMF header guard which was poorly designed and not only didn't cover enough of the header (more burns), the standoffs they used both cracked apart. It took over a month to get the same junk replacements from FMF. Apparently the aluminum spacer provided by FMF for using the stock header is also known to deform.

I went ahead and purchased the quiet insert for the PC4 and it too had major issues. The holes didn't line up and after fixing that the longer bolt provided clearly wasn't long enough as I found out on a backroad when my muffler spit it out. A longer bolt helped, but I had to check it every ride as it would like to back out (should have safety wired it, that would be attractive). I would have retapped for bigger threads but there were no access points.

Then all the mess with the FMF fuel controller and its bugs with certain settings that would completely cut out the throttle randomly. Probably dobeck's fault but still, I didn't pay money to troubleshoot this stuff. So that's my jaded opinion. I went back to the stock pipe which ended up only being a few lbs more and a ton quieter. Not quite the same snappiness, but surprisingly close in performance actually. Way too close for the money, hassle and noise.

I've been thinking about trying out the stock pipe just to see what the "butt dyno" says the difference feels like. I could definitely go for a quieter sound, but I do like the snappy throttle response. I am just too lazy to swap everything over... I know it would take all of 10 minutes. I should do it and repeat the sound testing for the sake of science.

I've also burned my pants on the FMF header. Thought about making a heat shield, never got around to it.

I'm not sure if the repack is "worth it" or not, but I do not regret doing it. I just wish I got the pillow packing instead of that tangled mess of awfulness.