Ok, didn't really know if it needed it or not, but the Ol' FMF Q4 has sounded louder to me lately. Last fall at the Bucky DS ride the guy running the sound check said it was at 99db a tad over the cutoff, but close enough to ride ( he wasn't sure what rpm to check the klx at so I don't know how accurate his reading really was). So since I'm planning to do a couple rides soon,and since I was shopping away at RMATV I decided to re-pack the muffler. I ordered the inexpensive LEXX fiberglass packing for 4 strokes. $7 if I remember correctly.
This is the first time repacking any muffler for me, so if any one has anything helpful to add, feel free. Really its only a few easy-ish steps. Start by pulling the muffler off the bike. Remove the 3mm allen bolt in the spark arrestor, and slide it out. Remove the 4 Allen bolts around the front of the can. Pull the muffler apart. It separates at the front where the 4 bolts were removed. It will have some hi-temp silicone at that joint so it may be tough to get apart. You can use a rubber mallet to tap on the rear mounting bracket while holding the mid pipe. Mine really didn't want to come apart, but I had neglected to take the spark arrestor out After I realized my mistake it came apart fairly easily.



I didn't think the old packing looked too bad, but what do I know. It was kind of a pain re wrapping the pipe since some of the packing needed to slip down into the front cavity where the mid pipe opens into the muffler. I wrapped and jammed it down in there the best i could. There was too much packing to all fit in the can so I had to trim some off with scissors. They recommend putting a strip of masking tape around the wrapped packing, but I didn't do that. I just kept it wrapped as I fed it all back into the can. As it got close to being all together I ran a strip of hi-temp silicone around the mid pipe where the two pcs join. I shoved it together and bolted things up. Some of the bolts were a little tricky to line up but nothing a little perseverance couldn't take care of.
Here's a link to the FMF how to repack. http://www.fmfracing.com/RiderSuppor...ngInstructions The next day after all my silicone joints were cured, I fired it up. It's quieter, not much, but probably right where it's supposed to be.
Dan







Spark arrestor.


Left over piece of the LEXX packing

 

Wow, looks like a disaster hope it all went together well for you.

M

 

Thanks for posting Dan.

It's little disappointing to see guts of the Q4. FMF web site says:
"The Q4 employs intricate chambers, baffles and proprietary multistage packing material making it the best performing quiet muffler available."

There doesn't appear to be any "internal chambers or baffles" at all. Just the run-of-mill perforated pipe packed in glass fiber. Borderline a false description of the product say I.

But thanks for posting the pictures and hopefully the re-pack helped with the noise level.

--
Mikko

 

pack it tight and it'll be louder but last longer, loose...visa versa

funny Finn, I was looking for all the tricks too, LOL must be that fat "power bomb" section in the middle of the core? unless we're not seeing something?

I have a new big gun and a Lexx sitting here and they are also "cherry bombs" the trickyness is in the end tip designs. The big gun uses quarter wave tubes in it's quiet core, the lexx uses side vented capped tube (a hemoltz resonator) like the crfx baffles. Both are straight through with their race cores.

 

My Q4 tends to blow out packing pretty quickly, even with just the stock 250 jug and me not riding particularly hard. The big problem I have is glass fibers collecting around the screen type spark arrestor and gradually choking it off. I have to pull it out every few rides and dig out all the fiberglass.

 

Also remember that adding a FMF header is another way to quiet it down a few decibels. The expansion chamber acts like a little muffler.

 

This is funny. Dan888 you read my mind. I sat down here @ the computer today to write about my experience today with the Two Brothers M7 repacking I did today.

I was thinking about ordering one of the tips for the M7 to quiet down the pipe a bit. Trying to pinch a few pennys I thought I'd check the packing first. Wow I was surprised, there was almost nothing in it! After taking it apart I literally only had enough packing in it to cover the palm of my hand...No wonder why its so loud!

For years I have used fiberglass insulation on all of my race bikes and silencer repacks. So I headed to Home Depo and found the smallest roll of glass, it was a "small project" pack. About 18" wide and 3' long. I wraped that sucker up and put it back together with enough glass for the next repack. What a difference in sound quality and now no need for the quiet tip.

 

Yeah I figured some on here would like to see the inside of the Q4. Nothing high tech inside there as far as I'm concerned, not that I expected too much. The through tube is actually two layers of perforated tubing and the thing towards the outlet end is some type of steel wool type material wrapped in wire mesh. I wouldn't use the word "intricate" on the make up of this muffler.
Dan

 

I actually thought the packing inside mine looked OK. This muffler has about 2yrs on it and at least 2500 miles. I will have to keep an eye on it with the new packing, as it has a different makeup. If it acts up like you describe I may go with the stringier loose fiberglass FMF sells. I have thought about using regular old insulation like slippery 750 used. ?? maybe next time.
Dan

 

The stringy "silent sport" stuff usually last longer. SS scour pads last the longest but don't attenuate the sound as well. Ceramic rock wool from a wood stove shop works good if you can get the stuff that's soft not brittle.