A motor need 3 things to run. Air, Gas, Spark.
If you have checked that air intake and found it to be clean then you should be getting air. CHECK
You cleaned the carb and check it for proper flow before putting it back on the motor, right. Then you are getting gas (assuming the tank isn't empty) CHECK
The only thing left is spark. Go down to your local sears and ask for a spark tester. They should know what it is and should have one. (Did when I got mine) basically all it is a item you plug into your spark plug wire then attach the other end to the spark plug then while kicking the bike watch for a spark, if none appear then there is something wrong with the ignition system. Usually best to leave that to the mechanics, as you can quickly screw up a motor if you don't know what your doing. IF you do see a spark then one of the things above isn't making its way all the way through to the engine.
This could be due to a bad valve.
If you want to know exactly how this works go to http://science.howstuffworks.com/two-stroke.htm