Hey, I just got a 400ex today!! Its a 2001 and it came w/ a pro circut t-4 pipe. However, the previous owner didn't rejet the bike or put on a new air filter. I was wondering if its necessary for me to rejet, or if i can just ride it with out rejeting and not cause damage to the engine. Thanks.

 

Come on guys, I know someone must know the answer.
Thanks

 

Yes you have to rejet. You also have to cut holes and the airbox lid and it wouldn't hurt to get a performance air filter.

 

You should rejet the quad for sure because of the pipe...but you DON'T have to cut holes in your airbox lid...if you want more flow it's not a bad idea but if your riding in deap water that would be a bad idea...a UNI filter would help some..just make sure whenever you do something to the exhaust, or the intake you need to rejet...

If you continue to ride with lean jetting it will cause excessive heat buildup, premature engine failure, can melt a hole in the piston....all bad things. Always rejet.