it just want start sometimes

when i first got my 82 200s atc a couple of months ago the spark advancer broke and caused me alot of problems. i finally got it back together and it ran great. but then the next day after riding i tried to start it up to put it in the garage. it would not start, not even a hit. about 10 minutes later it cranked right up. then i went about two weeks without it happening again. i changed my oil yesterday and afterwards it would not crank, no spark about an hour later it cranked right up. it then happened to me today 3 times. and the third time it actually died while running. i inspected all wires but could not find anything fraed. any suggestions would be great.

There is a little black "box" under the tank attached to the forward part of the frame, I thinks its the CDI box? Anyways take something like a small hammer and GENTLY tap it a few times. A friend of mine has to do that to his all the time and after he taps it, generally it'll start right up. His 200S was doing the same thing.