1.) Do you have spark?
If so, then put a few drops of fuel into the carb throat, or alternately the spark plug hole (while you got the plug out checking for spark). Does if fire but not stay running? Time to check the fuel flow....can you see it in the fuel line/filter? Did you push the "tickler" on the carb? If you have fuel and spark, all you need is air.
2.) No spark? check all connections and make sure you hooked everything up right. Still no spark? Call the seller (dealer).
3.) If you have fuel and spark, all you need is air. Is the air filter blocked or closed off in some way?
If you have spark, and you have fuel, and it is still not starting, then..The only thing it can be is that you have the black and the blue wires from the mag to CDI reversed. That puts spark 180 degrees out of phase and it will not start.
But..But..Keep in mind this. You can have a weak mag that will show spark with the plug removed, but when the plug is replaced and under compression, it will not spark.