Alright my bud just bought a 97 kx125 and it ran fine when he first picked it up, absolutely no bogging. When we get back and started it up it started bogging when riding in first gear at about 1/4 throttle. He shut it off and we were going to see what the problem was a couple days later. Just for kicks it started up and everything seemed fine, he rode for about 45 minutes and then just cut out. It wouldn't kick over. We replaced the spark plug and it is getting spark. Air filter is clean, we poured about a teaspoon of premix down the spark plug hole and back fired once. Tried bump starting it in 2nd n still nothing. Took it apart and seems like its getting gas flow thru the carb, the reeds look good (were a little stiff, thought they should flex a little), there was also a small metal chunk behind the reeds which makes me wonder how the cylinder and piston are. The owner also said he replaced the piston and was partially broken in, wouldn't think 45 mins of casual riding would cause this problem. Any info or sugguestions would be appreciated.