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Why is my XR400R burning up muffler packing?


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My XR has been burning up muffler packing in like 200 road miles. I have a CHM round tube muffler with their quiet insert and it's super loud. I drilled out the rivets and there was a scrap of packing material left in it. The rest came out in teeny tiny balls of melted fiberglass.

I bought some FMF muffler packing, cut it to the right length and width, rolled it up over the screened tube and riveted it back in.

Went for a supermoto road ride this past weekend, about 240 miles. It was quiet to start with, now once I'm home I ride it around and it's super loud again. I bet there's just some scraps of packing left if I pull it apart again.

My bike is jetted to run at sea level, and the plug color and performance at sea level is correct. I went for this ride from 4000 to 10000 feet this weekend and it ran real rich the whole time, I didn't bother to rejet. ๐Ÿ˜ Could the rich running have been flaming up in the muffler and turning the fiberglass into little tiny balls of melted glass?

I can't think of any other reason it would do that other than the fiberglass packing was in direct contact with flame.

Any ideas? Thanks!

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A rich running engine can heat up the exhaust as you surmised. If I understand your post right you are burning up packing at sea level also. Maybe it's poor quality packing. So it doesn't sound like the rich condition is the reason...at least not the entire reason..

Darrell

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Did you wrap the core with steel wool first? I have heard through some online sources that without the steel wool layer 4 strokes will blow out the packing really quick.

Here is a cool video on repacking a 4 stroke muffler.

No. I'd never heard of that. But I will be doing that this time. Thanks! Great tip.

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Good tip Alex, Thanks.๐Ÿ˜
No. I'd never heard of that. But I will be doing that this time. Thanks! Great tip.
You can buy packing in cells or pillow style but after watching that video I think the steel wool route is a much better way. I've never seen it done that way and I have a machine I will be trying it on very soon.๐Ÿ˜

hey your welcome guys! glad i could help. hope it works. :cheers:

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  • 2 months later...

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