Silencer packing

Blown silencer packing will usually make the revs break-up early. Thats because of excess turbulence in the tail-pipe, effectively blocking the flow. So I suppose that it would make the jetting seem rich because the revs are breaking up early, but if you lean the main jet, you'll probably burn a hole in the center of the piston crown. You see the blown packing causes turbulence and a flow problem which makes the piston crown run hotter, less fuel to cool the piston will push it to the melting point.
Small displacement bikes require more frequent service of the packing material. Try the Silent Sport brand of packing material, you can buy it in a bag, enough for a few packing changes.
Good luck

Check the Dyno link below. The sniffer we had in the tail pipe confirms what Eric said. With the packing blown out the bike ran richer.

Dyno

380EXCman, even though I use Silent Sport, when servicing my silencers the packing is always blown through in the areas of the unevenness of the loose fill. The pillow pack method is better but still leaves gaps along the silencer core. While Silent Sport is a long lasting packing, I believe it has a bit of a performance problem also, as it does not promote an important even core pressure. I think I'll try some Performax. I have some dyno time upcoming and if time allows I'll test Silent Sport vs Performax. :thumb: