I have a 2001 400ex I just bought this past weekend, it has fmf powerbomb pipe, hmf slip on exhaust, k and n air filter, no air filter box lid and it idles fine but when you go to ride it and you get past half throttle it acts like it’s cutting out, do I need to rejet my carb? If so how big?

 

Welcome to the forums.

I'd clean the carb and see what jet is in there now. Could be something as simple as a little dirt. You'll need to do more than just spray to get it clean. A small wire to make sure you got the seat for the jets clean can make a big difference.

 

yea, first clean out the carb and if it is still off, then rejet. I don't know the size