Repacking Cobra F1's
I have no idea when the previous owner put these on the bike, but they weren't loud or showing signs of needing repacking. The reason I did it is that a couple of rivets had worked themselves loose and created the most obnoxious buzzing while riding. I figured since I'd have them apart to replace the rivets I may as well pack them. There aren't many posts on the subject, but luckily the process is more or less obvious.
I started by removing both pipes from the bike and drilling out the rivets. Once the rivets have been removed, the cans can be slid off the pipes. Carbon buildup can make them sticky, but I found that twisting the cans on the pipes allowed them to be worked off fairly easily. Once the cans were off, I removed the old packing. As it turns out, there was a good bit left- I'd estimate 2/3 of the original material was still inside. Apparently Cobra uses some adhesive to hold the packing to the pipe- but it came off very easily with a copper scouring pad. After removing the old material from the pipe and can, I used a small screwdriver to open up any holes in the pipe that had become clogged with packing and/or carbon.
Wrapping the pipe with the new packing material could not have been any easier. I've seen a few posts from people that have used the loose fiberglass filler in their pipes- I chose the Moose Racing brand packing that comes in 12x16 in. sheets. As it turns out, one sheet is just the right size to wrap the pipe to a snug fit in the can. I wrapped each pipe, and tied it down with mirror hanging wire that I got from Home Depot. I then slid the can back over the packing, twisting it as I went so as not to catch the edge on the packing. I lined up the holes, popped in new rivets, and that was it.
My total expense for repacking my mufflers was 10 bucks for a pop riveter, 3 bucks for a box of rivets, and 12 bucks for two sheets of Moose packing. Total time spent was about an hour. If you've got F1's, and they're loud or buzzy, it's definitely something you can do yourself- quickly, and on the cheap.