Here's my KX500 out on the ice starting regiment.
If it's in the teens (F) and higher all's you need to do is introduce a bit of "raw" fuel into the intake. Lay your KX500 hard over on it's left side until you see some fuel exit out the carb overflow. Now pull the choke, and after about 3-4 kick she should lite right off. (This is all assumed that you have favorable "winter" jetting). If you are trying to start a KX500 with stock jetting in very cold temps, just keep kicking your brains out cause it will never start....
Another tip, if temps are in the single digits, even I sometimes have a hard time starting. Bring a plummers' propane bottle and warm the cylinder prior to kicking. It makes a HUGE difference in startability !