I have a 2003 Z400 and the ignition seems to break up while under load in the mid range then clear up and runs great in the high r's till you shift. It does it in every gear. Its acts like you are hitting the rev limiter but way early. I have cleaned the carb, changed the plug, and drained and filled with fresh fuel. I am leaning towards a cdi since it does it at the same rpm in every gear but I'm not sure. Anyone had a simular issue. Poss. bad coil??? Thanks for any help.

 

Check the water level in the battery and see if it's low...........if it is replace the Rectifier Assy. It's my guess because that's what was wrong with my ATV and it had the same symptom as you said.

 

you may wanna mess with the needle clip position in your carb (i'm assuming it's a vm or tm type carb that has an adjustable needle, and not the overly-complicated vacuum diaphragm type carb). move it down one or two notches, try it, and see if anything changes.

 

My batt has been getting weak. I did get lucky and found a coil and cdi on ebay for 30 bucks.