i have a 2004 z400 with the 440 kit in it. i bought it off of a guy and it needed a shift shaft seal so i did that. i started it up runs great except when you really hammer into the gas it starts popping and sputtering. what may be the cause of this?

 

most likely jetting is off, when you bought it did the guy say anything about rejetting it or anything? also what pipe is on it?

 

the guy did not say ne thing about that. it has an hmf pipe on it

 

seems like the jetting is off then, prolly needs a few sizes bigger on the main jet

 

no the guy did not say any thing about rejetting it. it also has an HMF pipe.

 

ok how do i know how much bigger to go on the main?