So I just bought a 2001 400ex with 440 bore kit. It has a white bros exhaust slip on. What size jet would be used with the bore kit and the exhaust. The jet that is in now keeps flooding the carb unless it's floored and I do a lot of trail/woods riding and it's just not working out when there is no low end power. Could anybody help me out?

 

Your best bet is to contact a company that specializes in carb services and rebuild kits. Your problem may not be a simple jet change. In years past I used the "UNI" company, contacted them with the engine specs and any mods done to it along with any issues I might have. They would then send me a carb rebuild kit with all the instructions for setting up the carb and proper jet sizes. Every kit I ever bought from them worked very well and instructions were easy to follow. Why guess, when for a few bucks you can get it right.

 

I typed in UNI carb rebuild kit but I don't think I am finding the right things...

 

It has been a few years since I used them last but I do know they are still in business. They specialize in air filters but always had a carb service as well.
Try looking for UNI air filters and then give them a call. I also know there are other carb specialist companies out there just haven't had experience with them.

 

Flooding out could be float needle related also. Good Japanese kit here if needed.HONDA TRX400EX TRX 400 EX CARBURETOR CARB REPAIR REBUILD KIT 1999-2004 2000 2001 | eBay Plus Jetsrus has individual or a jet set.https://www.jetsrus.com/a_jet_kit_at..._1999-2008.htm