Ah when I had that problem on the first try I had a wire loose. My very first guess would be the wiring from the engine to the coil. So here is my suggestion. unhook the kill switch, then hook up the other to wires. and give it a try. Has directions on how to test the coil for spark in the classic instruction section.
The other time I had this problem I did not have the coil wire attached to the coil end correctly. It takes some work to screw it into the little nipple that is inside the coil case. I didn't get it in good after I removed the wire for something else.
Give those to things a try first, If it isn't either of those take a look here....http://motorbicycling.com/f3/troble-...spark-197.html
When I first installed my engine I was so apprehensive I thought everything was wrong and I wanted to trash it. It's take a little time but it will all work out