a friend of mine came over today with his z400. i jetted the carb from a 130 to a 155 and cut a 2-3/8 hole in his airbox lid stock exhaust. he said that it is running a lot better. well after he left he and his nephew showed up an hour later wanting me to jet his 400ex so i jetted it from a 148 to a 160 and cut the same size hole in the lid. the dang 400ex was beating this z i couldnt believe it so i got on the z and sure enough he outran me. i have been around bikesmy whole life(32 yrs old) and i have been drag racing for 4 years now so i know a little about speed but what did i do wrong if any

 

if the only mod to the 400ex is the drilled lid, put in a keihin 152 mainjet and it will be quicker than it is now. i have spent numerous hours jetting 400ex's. you will notice more power mainly up in the higher gears but there will be more. i am not sure on the z. they run mikuni carbs and i never messed with those. i have seen some z's quick and others that were slow.

 

Most likely cuz you jetted the Z way too fat.. I wouldn't go over a 145 main with the mods you did. Then again, most Zer's I talk with jet way too fat themselves... LOL!