'00 WR400 jetting (FMF Specs?)

I'm running a powerbomb and Power 4 pipe, FMF says to run a 180mj, needle position 4th from top, stock pj, air screw 2 3/4 turns out. I've run as high as a 178mj with these specs and response sucks. Crack the throttle and it won't pull. Could this be an accelerator pump problem? I know the '00 has an updated carb design from earlier WR's.


Don't know what your altitude is but the below settings work great for me.


Maybe it is waaay off, but it's what FMF says to run. I'm around 600-800 feet above see level, so the 150 range for a mj sounds way off to me. I had a 168 in it, and that was too lean, so up the jet ladder I went all the way to 178. 180mj is what FMF says to run, so I guess I'll give that a shot.


I first put a Q on my bike and left the stock header. It had a 168 main in it. After install of the pipe, it was so lean it barely ran and backfired like crazy. Went to the suggested 180 main and 2 3/4 turns out per FMF and it was jetted perfect. Then I installed a powerbomb SX header about 6 months later and have had to go back to a 162 main. The new header really seemed to richen it up. Lots more power on the bottom, but did dramatically affect my jetting. I ride at about 750-2000 in elevation as well. Hope that helps.

It does, thanks Kirk W. I got home from work today and decided to see if I could get it squared away for riding tomorrow. I swapped out the 178mj and incrementally tried smaller ones. No luck. Then I put in a 168mj (in it from the guy I bought it from) and put the lid back on the airbox like he had it. Still bogs like a mofo! The 165mj is stock. I might try a 170mj tomorrow with the lid on and see if it will bog at WOT.

If anyone has any advise for me I'm all ears. When testing it is warmed up so that's not the problem. I'm running premium pump gas so that shouldn't be a variable. :)

Your problem is needle to 3/4 throttle. Try lowering the needle a clip (clip up to 3) Sounds like it's too rich low. The pipe will lean it out at WOT. You may need to adjust your AP to less than one second and explore smaller pilots. The JD kit and instuctions would be the quick remedy, otherwise read all the pages of Jetting Q's..Good luck :)

Okay, I got it figured out. The Power Core 4 from FMF necessitates a switch to a 180mj. That's the number FMF gave me. But I also have a Powerbomb that I'm running which has drastically changed the jetting. The main jet running the Powerbomb should be a 162mj, just like KirkW said above. Hey FMF, get your head out of your A$$!! Thanks to everyone for the advice.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now