Are you sure your handlebar is 28.6 mm? That's a really unusual bar size. Common sizes I'd expect to find on a Fuji would be 25.4, 26.0, or 31.8. I don't know what year your bike is, but according to the Fuji web site, a 2014 Fuji Track Classic came with a 26.0 mm handlebar.

28.6 mm is the same as 1 1/8" though, which is almost certainly the size of your fork's steerer tube. One end of your stem grabs the steerer and the other end of the stem clamps the handlebar. Is it possible that's where you're getting the number from?

Anyway, if you want to use a handlebar with a 25.4 mm diameter, you can do it, but you'll need to do one of two things: You can replace your existing stem with one sized for a 25.4 mm bar or you can use a shim to fill the gap between your current stem's larger clamp and the bar. Here's one that'll allow you to use a 25.4 mm bar in a 26.0 mm stem.