I HAVE A 1995 KAWASAKI BAYOU 400 4X4 THAT WILL NOT START WITH THE STARTER, WHEN THE ENGINE IS COLD. THE SUMMER WARMTH HAS NOT MADE IT ANY BETTER. YOU HAVE TO KICK START IT EVERY TIME WHEN IT IS COLD. ONCE IT STARTS AND HEATS UP, IT WILL START WITH THE STARTER WITHOUT ANY PROBLEMS.
IF IT SITS AND GETS COOL AGAIN, YOU HAVE TO KICK IT AGAIN.

It sounds as if you may have a bad battery that begins to looses charge once the engine is off. While you equate the problem with the engine being warm, it may have nothing to do with it. Because you are starting the engine soon after the magneto has been charging the battery, there is still enough charge to turn the engine quickly enough to start.

I replaced the battery. even tried an on board charger, which I plugged up every night. Still the same problem.

Have you checked the valve clearances? They can make it more difficult to start the engine if not within tolerance and will change somewhat as the engine warms.