repacking stock silencer-dB ??

[toolie]

How many dB would a stock 86 400XC put out if freshly repacked?

Last year I rode an OFFROAD ONTARIO enduro and was a little over the max. allowable of 94dB. Luckily they let me slide, not like I have to rev the bike hard in the woods.

 

[justintendo]

do you have the spark arrestor installed? they knock a good bit of the sound down.. is the silencer still stock length?

 

[toolie]

Yes, still original length, I have not opened it up yet.

I will in a few days. I think it's really plugged up.

 

[justintendo]

Yes, still original length, I have not opened it up yet.

I will in a few days. I think it's really plugged up.

oh this thing hasnt been repacked yet? it will quiet down a great deal.

 

[suprize]

as the packing fills with oil and pooh, the muffler effectively becomes a straight through "stinger pipe". loud... packing with new packing or steel wool will take the bark out of it. make sure the perforated tube is cleaned well before repacking. you will notice it pulls harder down low and signs off a tad earlier..

 

[toolie]

OK, thanks.

I'll let you know how bad it is once I have it apart.

 

[yellowbronco]

Yes! Definitely let us know how it goes. I have an '84 WR400 that's bone stock with only about 2500 miles on it since it was new. I'm certain that the muffler has never been repacked and I'm annoyed at how loud it is. Hoping a simple repack will help and I won't have to adapt a newer muffler.

 

[justintendo]

Yes! Definitely let us know how it goes. I have an '84 WR400 that's bone stock with only about 2500 miles on it since it was new. I'm certain that the muffler has never been repacked and I'm annoyed at how loud it is. Hoping a simple repack will help and I won't have to adapt a newer muffler.

repack the muffler..it will be a help and if its never been done be a big performance boost.

 

[Bigbill]

Great post I heard the sound guys are showing up at our local riding spot even though there is no event going on. All we can do is repack the muffler.

 

[suprize]

I have an '84 WR400 that's bone stock with only about 2500 miles on it

Only!! That's a looong way for a dirt bike, its 30 hard weekends of riding or close to two racing seasons... you need to get busy!
rip the top end off and check the ring gap and piston clearance
regrease the headstem and swing arm bearings..
While the bike is in bits ... change the fork oil (and seals) and service the shox
check wheel bearings and grease brake pivots
lube the cables and throttle grip, replace the hand grips
while your at it, best get a new airfilter as well and change the gearbox oil

and above all, don't forget to service the muffler

pull it to bits, clean it with a solvent, wire brush the perforated tube to remove all carbon or heat it to red hot and bash it with a bit of wood (gently!)
reassemble with quality packing or steel wool...

now you can ride it

 

[yellowbronco]

Awesome!
Gonna leave work early and get right on that!

 

[toolie]

Update;

Pulled the silencer packing off and no spark arrestor, I thought it would be internal. Obviously I'll need to find one, hopefully someone here can point me towards a replacement. What are the chances of finding something oem.

Something I did notice is the packing was very tight, and actually not that fouled.

 

[Eurofreak]

Oh Suprize ya talk so dirty!

 

[Eurofreak]

What does the spark arrester do to the powerband?

 

[justintendo]

What does the spark arrester do to the powerband?

pretty much decreases power all around..sometimes maybe adding some bottom. they can help you be legal in some areas and many designs cut sound quite a bit. non powervalve bikes will always be louder than newer bikes. that huge exhaust port is there all the time...

 

[toolie]

Oh Suprize ya talk so dirty!

 

[fran...k.]

I have never been able to repack a silencer and have it as quiet as expected and I generally use one sheet and a part of another to fill it. Just due to the length not over stuffing. How it is measured might matter, at a real enduro (at least one I recall) they seem to put a device that detects vibration hence rpm, look up the bike's max hp rpm in some printed document and then run the engine at no load at half of that. The one vintgae enduro I entered they just used a stick to measure the distance from the exhaust to the meter. A power valve in the closed down position will greatly decrease the pressure at the time the exhaust opens. If you work a check you have an idea of what you can hear for a long time before it shows up. If you spectate on a hill section you can also make observations.

 

[Eurofreak]

I was considering a down turned exhaust tip to lower the sound a little. For emergency noise reduction at enduros we would get a section of inner tube and wire it to the end of the silencer. It mad a weird flapping noise but would reduce the sound. Think whoopee cushion

 

[fran...k.]

Now that you mention they did that inner tube on the end of the silencer thing to my bike at one enduro or perhaps turkey run, in western Mass when I had the xc500. They had a few ready to go.

 

[suprize]

I put a down turned down exit pipe ala kdx 200 on my muffler. pretty sure it helped the bark. don't forget when these bikes were made, limits were higher. in aus it was 98 dB I think. interesting, a stock dr 400 in 2005 was well over 100 db