I built a bike for a guy this last fall using a new 66cc HT 2 stroke engine. For the life of me I could not figure out why the darn thing was not firing and one of the first things I did was try swapping the cdi which didn't work. Got my tester out and found that the blue wire that is soldered onto the megneto was a cold solder from the factory and not making a connection. I got my solder iron out and redid the solder connection on the magneto and low and behold the problem was solved. A simple fix that didn't cost me anything but a few hours of head scratching. Might be something you want to check as well.