[ThumperHumper]

My friend has a 1993 yz250. It has this annoying non stop bog only when you pin the throttle. After you ride it for an hour it goes away. It only does it in the high rpms. The bike is actually a really nice bike for a 93 its just that damn bog. Also, he changed the outer transmission seal,(behind the countershaft sprocket) and it still leaks. Any ideas??????

[04 crf450]

try cleaning the carb and check the compression it could be low