Keep in my this is my first motorcycle..

Total noob question:

Does the stock muffler need to be repacked?

 

nope.

good luck with your bike.

 

Why is it that you have to repack the aftermarket mufflers?

 

The insulation inside gets old and burns up. As it degrades your bike gets louder.

 

Many stock mufflers do not use packing material and therefore don't need repacked.
Many aftermarket mufflers are just the opposite. They have packing material and require repacking. Why the difference? I don't know for sure, but I suspect because the aftermarket mufflers are lighter and flow better than stock models; the aftermarket use packing to reduce noise levels whereas stock uses series of baffles. The packing material, fiberglass from what I've seen, breaks down and blows out with exhaust becoming less effective.

 

So if one does not care about noise, then there is no need to repack?

 

My dirt bike shop mentioned the silencer canister can be heat damaged if run without packing. Power will also suffer. http://www.supertrapp.com/images/pdf...acking-FAQ.pdf

 

I bought my fmf pc4 around two years ago.
About a year ago I bought some packing material, although I never got round to repacking the exhaust because I could never undo the exhaust bolts.

 

I just tore my fmf powercore 4 apart for the 2nd time. First time i put about 8,000 miles on it before repacking and the fiberglass was about 95% burnt, very little white left. This time its only been 3,000 and its already around 50% toast. I think a repack a year should be normal maintenance, its $10 for the fmf fiberglass and about 30 minutes of work.

 

cegusman,
What is your riding style? I understand the harder the bike is ridden, the more frequent repack is needed. Mine is probably due.