09 yz450f exhaust issues

ive got a 4 month old, 09 yz450f (bought new), stock muffler packing burned out in less than one month, ive tried several good quality repack materials but packing completely burns out in 2-3 hours. jetting was stock, does not appear to be lean but i have just richened main jet from 160 to 165, in an effort to lower exhaust gases temperatures....anyone have this problem?

Problem is, its the stock exhaust. Dump it, save it for resale/back up, and get an aftermarket exhaust.

thank you for your opinion, but im looking for an actual mechanical explanation....ive not read where others are having this problem.

Just a thought here, maybe the mechanical baffles in the muffler blow out the packing faster. I know the YZ is the only bike that comes with the cones built into the muffler which I think directs the exhaust into the packing. Try looking up Bristol Core, I have heard good things about their packing kits.

The packing kit you use needs to have a steel mesh inner liner in it or you're wasting time and money. The DRD pro pack is made like this. The '08-'09 muffler blows packing out more rapidly for the reason the motoryan suggests; the baffling cones divert the exhaust into the packing more directly and forcefully, and it's just hard on things. "Less than a month" seems quick, though. BTW, a richer jet will not necessarily lower exhaust temps.

Weird. My stock exhast packing has lasted a long time.

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