My old man has a 97 kawi 400 and we were out on the trails today running along and when he would run along for a while about 3/4 throttle it would start to backfire, let off to 1/2 for a few minutes and the back up to 3/4, and would be good for about 5 mins when it would start to backfire again. the bike was not running hot, does anyone know what the problem is or had this happen at higher speeds. Any help is appreciated, thanks.

 

This sounds very familiar to my problem. Sounds like fuel starvation. Time for a good carb cleaning, and check out your petcock gasket, if its missing or in chunks then its time for a really good carb cleaning. I reccomend a fuel filter also. Could be something stupid like bad gas also. Good luck.