I want to give my EX more horsepower. I'm going to rejet, modify my airbox, and put a K&N air filter on it. I do alot of woods riding with my friends. Should I buy a slip on pipe or would the stock be enough, I'm not goin to mod. my engine any so I was just thinking of going with the Yoshimura slip on. Also would a 14 tooth sprocket help, I don't want to loose alot on top end though because when my friends want to race I like lettin them in the dust(oh yeah)...any help would be appreciated!!!!

 

YOu wont gain a whole lot with just the filter. The slip on will help a bit. You should mod your air box also and you will have to re-jet. With those you might get a couple of horse. Dont expect to much and you will be happy with any mod, expect to much and you will always be disapointed! Keep that in mind with these machines.

 

Does anyone else know anything on this??

 

If you have the money get a complete exhauset system. The complete system will make a big difference over just the slip-on. Instead of putting holes in the airbox lid, put the tabs down on the front of the airbox and then put the lid on top of them and still fasten the 2 rear tabs. Try about a 152 main jet and a 40 pilote(can't speel). With these mods the 400 will run just about the same as a 440 in the woods.