No an expert, but all an ICE needs to run is fuel, air and spark. If you've got spark, shoot some starting fluid in there and it should fire. If it starts and then dies then you've got a fuel delivery issue. If it doesn't do anything, then you don't have good or consistent spark. Also, if you installed an auto-decompressor (sounds like you did), it should be working fine if it's hard to turn over like you say it is. CDI sounds suspect to me if you put a used eBay one on. They're prone to failure anyway and you've got one that (in my mind) is suspect anyway. Their failure can be intermittent. Take a video of you trying to start it. "No start" symptoms can vary greatly and mean a lot of different things. Is the gas on??