Site upgrade in progress... Core site functions are working, but some non-critical features/functions will be temporarily unavailable while we work to restore them over the next couple of weeks.

Please post any bugs you encounter, but before you do, check to see if it's already listed.

Thanks for your patience while we work to improve the community.


YZ426 Carb on 99 WR400 (Wrong Needle?)

1 post in this topic

The bike:

1999 WR400F
Grey Wire Cut
Pro Circuit T4 full exhaust
Stock air filter with cover removed
02 YZ426 Carb (2nd gen FCR)
MSR Extended Fuel Screw
FMF Stage 1 Kit with 170 main, needle on 2nd clip from top, all else stock
Riding at around 1500ft when test riding the bike, won't exceed 3500ft for most riding, & currently 60-70*F

The Problem:

The bike misfires at about half throttle in every gear. It's fine at lower & higher throttle, but around the middle it starts to sputter & sound almost like it's hitting the rev limiter (but slower & less consistent). I admittedly have not tried a different main jet yet, trying to confirm or deny another possibilities first, as it has the main jet (170) that nearly everyone from 0-3000ft altitude is running on the WR/YZ 400s & 426s (based on the Jetting Database thread). I have tried unplugging the TPS & it made no noticeable difference. For the WR/YZ guru's, I'm wondering if it could be the wrong needle for the WR. As noted, the carb is from a YZ426, & I've read somewhere before that the WR with YZ timing requires the YZ needle to run properly. I ordered the jet kit for the YZ carb since the jet types are not all the same from the 1st to 2nd gen FCRs, but now I'm wondering if I need to get a needle for the WR426 (same carb, but maybe different needle?). I checked the spark plug & it's a little on the white side, but it's damn close to dead on. Before I spend more money, am I correct in thinking that the YZ & WR have a different needle? Will a 1st gen FCR needle from a WR work for the 2nd gen carb (still got my old FCR)? Anyone else had this particular problem or have any input other than going with a bigger main jet?

Edited by samburger

Share this post

Link to post
Share on other sites

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