Like Bob said, it's a common problem with a gear deep in the mechanism that starts slipping. It's a good idea to disconnect the cable when that starts happening because the gears can lock up which will cause other damage - like stripping the nylon helical input gears. Those suckers are $25 each if you can find them.
Not worth taking the chance.
It's possible to fix it yourself - just depends on how mechanically inclined you are and your enjoyment of solving puzzles - like of the Chinese kind. How's your patience quotient?
As for Bill's 80mph speedo, I agree - if the bike is an early build, it's quite possible it came with an 80. I wonder how long it took to run out of the 80s and get back to the 120s?
On another note, Bill asked why no one likes the 80s and I had a hard time answering that one. I know, for me personally, that the 80s just don't look as cool as a 120. That, and the bike is good for more than 80, so why not have an instrument that measures the full range?
