I have a 78KE125 and it will run fine unless I drive it for some time over 6000 rpm. Then it starts to cut out unless it is under around 4000rpm. But it will go all day unless I need to ride a stretch going over about 50mph which is about max for this thing. I've cleaned the carbs and have tried changing the main jet but to no avail. Compression is not as good as it should be but I can't understand why it only runs rough at certain times.