The KLX is a beast to start when hot or after a fall. there are several techniques and/or mods you can make to help this problem.
1.) hotstart valve,
2.) Tee-vents on the carburetor,
3.) turn off the gas and lay the bike on its side to let the excess gas drain out,
4.) make sure you have the bike at top dead center before you kick it over.
5.) hold the throttle wide open and leave it open while you kick, if you suspect the bike is flooded
I have had 3 KLX's and am thinking about getting my 4th in a few weeks, they are a great bike, but the occasional hard starting is a known issue.
try this website:
www.planetklx.com, you can also sign up for the owners group, there are a lot of people there that know a lot about the KLX.