so the throttle response is good and normal for first and second gear, but as soon as i get into third and up in the higher rpms and over 1/2 throttle it stutters, bogs and won't gain anymore rpms very easily? i took the carb off and everything seems alright, i didn't go to in depth cuz it was running good a few weeks ago, all the jets are in place and tight and it is very clean? any ideas?
thanks

do you have any mods that would cause you to change the jetting? sounds like a jetting issue in the midrange

i really don't think so, it is bone stock, and was running great for over a year then this started the last time it was ridden. so i don't know, i am almost thinking something electrical, but.....idk

clean out your carb... its possible you got a particle in there blocking one of the many passages

Did this ever get figured out? I got a budy with a z400 that started running bad lately. He hasn't changed anything on the bike at all. He's had it about 6 months and all of a sudden it doesn't even like to run.

my old z400 use to get water in the top of the moter, where the spark plug goes in. It was not sealed completly. It would just quit at anygiven time and not start back up for a while.