What do I need to do? I'm guessing this summer will require the following:
- Chain (how do I know?)
- Valve adjustment (how do I know?)
- Brake pads (do I need to do the rotors too?)
- Brake fluid (or no?)
- Clean carbs (I'd like to rejet... so this may be a side benefit)
- Tires (maybe)
Chain - when it can't be adjusted to maintain the proper slack anymore, or if it's damaged. Replace the sprockets when you install a new chain. If you don't, the new chain won't last long.
Valve adjustment - SHOULD have been done at the initial 600 mile service and again at 7500 miles. (Many dealers will ignore the valve adjustment @ 600 though.) Suzuki calls to check it every 7500 thereafter, but after 15,000, it doesn't usually change anymore. I check mine annually (~10,000 miles). You should have slight valve train noise. If it's too quiet, they're too tight - and this is more common than them getting too loose, especially in the first 15,000 miles.
Brake pads - There's wear indicator grooves in the pads (or at least there is on the B12, not sure about the B6), when they're smooth, or close to it, it's time for a change. Depends on how you ride,, but 15-20K miles isn't uncommon life for the stockers. Rotors should be OK. You'll feel it in the lever if they warp. +1 on the HH pads!
Brake fluid - At 4.5 years old, it should be changed. Fork oil, too. (Actually should have been changed several times by now.)
Clean carbs - if you let it sit for a month or more at a time without fuel stabilizer, it would be a real good idea. If you're going to install a jet kit, this would be a good time.
Tires - With 10K miles, they should be about shot by now, if not, their 4.5 years of age should be starting to show even if the tread is still there. Even if they aren't cracking, the age of the rubber is at a point where they should be changed. I'd be budgeting for some new shoes for your baby.