[Didn't search for this, but I really didn't know what to search for]
I've got a mezzo folding bike that uses fairly standard parts. I've had it serviced by several different people, so when I had it serviced last time, the guy told me someone had put a 7 speed shift in despite having a 9 speed cassette I took him at his word. He told me he'd adjusted it to give me the 7 highest gears, which I had been ok with until I went to a hilly part of my city and had to get out and walk.
So today I finally took a look at my bike. Both the derailleur and the shifter are original. I'm trying to sort this out with the help of Sheldon Brown - it's tricky - but something that isn't on his page: My 9 speed shifter only clicks 7 times. Basically, when I am changing down I have two cogs left, but only one click, if you see what I mean. How do I get my last click back?