The sliding pins are seized, meaning the brake is no longer "pinching" the disc, but just pressing the right pad against the disc. This is much less than half efficient!
Take the caliper apart, clean thoroughly and rebuild, replacing the seals and the rubber sliding boots as required.
It sounds scary but it's not, and you are lucky in that you have one of the most basic brake systems imaginable to learn on. Have a go through my reply here:
http://www.hondacb1.org/forum/index.php/topic,783.0.html