I have a stock z400 and was told changing my sprocket would improve the speed .IS this true? what sprocket should i go with and wrer do i get it?

 

13t front and 39t rear is a pretty good set up . If you just do the 13t front you will notice a lot of torq but you have to shift alot faster.

Your local dealer parts or moto shops carry sprockets or you can go through Rocky Mtn