Like the guy said, you are flooding it. When you drop the bike and pick it back up, turn the throttle wide open and hold it there. Kick the bike over about 8 to 10 times and then release the throttle and try to start it. This will clean out a flooded engine. Do not work the throttle or it will flood it again.
Do a search. There is a lot of information about how to start your four stroke.
Also, if you haven't done so already, check your valve adjustment. A tight valve will make your bike hard to start.