Rich/Lean Indicators?

I own at 2K WR 400, and I'm going through the usual jetting B.S. and pulling my hair out all over the place. It seems that the 2000 comes VERY lean, it ran really hot new. So, I removed the baffle and airbox lid after break-in, and rejetted...and rejetted...., anyway, no luck. I went straight to 178/48/#4 Clip after removal of the baffle and lid. Apparently too rich, as the spark plug was black. At this setting, I had a wicked "fall on face" hesitation at low RPM when cranking the throttle open rather quickly (not too quickly however). SO, I've worked my way down to a 172/45/#4 and it still isn't right at all. Big miss even when moving if I crack the throttle open. Is it possible that the plug is fouled to the point where I'm not going to get decent performance? How do I tell? What does it mean when I get a backfire through the airfilter? Lean or rich? How about setting as far as jetting. Everything I've read is right around 172/45/#3 or 4, but I'm still running like crap. Any help with this would be SO greatly apprieciated! Thanks in advance...Scott Fisher

Have you adjusted your pilot screw?... To what setting? Throttle stop cut yet? Baffle removed? Need more info...

My '00 WR has a #45 pilot with pilot screw set at 2 1/2 turns (out is richer)with no ex. baffle. Try a new plug to be sure.

[This message has been edited by James Dean (edited 06-21-2000).]

James Dean, I have removed the baffle and air box lid, and also cut the screw to proper length. Those are the only modifications. I talked to the dealer, and he said that the red hot exhaust is normal, but if I can get it to run correctly without it running so hot I would be happy. What main jet are you running? I am considering a 45PJ/170MJ setup. I just went and bought a couple plugs today, hopefully one of the about will make a difference (I'm an ME student right now so I look up to you!!). Thanks for the info.


An ME student?... Great!

Don't expect the main jet to make any difference with your problem. It only meters fuel at 3/4 to full throttle. I have run my bike without a main jet before to confirm this, rode 20 miles no problem! Most guys run 170-180.(#172 in mine now) You must try adjusting the pilot(fuel) screw on the bottom of the float bowl. About 2 1/2 turns from fully seated is my current setting with #45 pilot jet and at 60F and 500ft elev. Needle clip #3 is stock, but it is lean at low throttle settings and transitions from idle may hesitate.(#1 is top clip slot) Many on the Forum have switched the needle out. DVP or EKP are good choices and are options from the YZ400/426. Familiarize yourself with the jetting tips in the tech section on Thumpertalk and the manual.

scott did you get sorted? info is a two-way thing.

hey Fischer. Yes, we have all struggled. Mine did the same thing (similar setup) until I lowered the clip on the needle one notch to 4. Use a fresh plug when making jetting changes to get a good reading of the new mixture. Yes, it will be hard to start with a fouled plug even if your mixture is good.

James dean seems to know his stuff about jetting, search in the posts for the needle discussions. If you need help moving the clip, drop me a line

Anyway the moment I adjusted the needle (172/45) and adjusted the pilot screw properly the hiccup was 95% gone. I still foul plugs after long downhill decents or extended slow riding, so further adjustments (needle change?) are still needed, but it runs incredibly well. The next step is to experiment with needle. One note about the fuel screw on the '00-on my bike one tiny turn of the screw seems to do a lot-turn it and wait for 10 seconds between turns to listen for the engine to smooth out. Good luck.

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