YZ426 Carb on 99 WR400 (Wrong Needle?)

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  • samburger

Posted February 02, 2016 - 08:17 AM


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, February 02, 2016 - 08:59 AM.


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