You will see right by that ledge on the second speed, there is a little metal pin that is to help it still catch if the plastic wears. Your second speed centrifugal clutch could very well be in backwards. Just look at the clutch and look at the second gear and remembering that it will turn counterclockwise when you are looking at it from the front, you want the clutch to open so that it will hit the ledge/pin ,not slide.
Its hard to explain and i dont have mine apart right now to post a pic.

Could you post a pic of the inside of your seond speed spur?