Jetting Problem, I think????

I have an 01 WR426 that the lid is gone, gray wire removed, uncorked, and is hard to start when cold if it don't foul the plug. When it does start it misses until completely warm, usually about 5 mins or so. The bike has about 650 miles, I never reset the trip meter. I replaced the MJ to 170, i think and the PJ to 38, if I remember correctly. Oh, Almost forgot I am in the coal fields of VA about 1900ft.


What did you change the main jet from ?? is it better or worse, give us more info.

If you still have the stock pilot air jet (75) then you maybe a little lean on the pilot circuit. Try using a 40 or 42 with the 75 pilot air.

Check my signature below. I run the coal hills in PA with elevations from 200 - 1600'. I highly recommend you read the thread " jetting Q's".

HEY ! Look at me, giving jetting advise. A Couple of months ago, I only knew the twisty thing on the right made it go. :D:)

I had gone to that jetting from stock, all jetting is still stock except for what I have mentioned, when I first got the bike. There was a miss in it until warm then it ran fine, I went back to stock jetting to see if that would help, wrong it was pretty sluggish, so I went to 170 MJ and a 38 PJ and got even worse, so tonight I went back to the 170 MJ and 42 PJ with everything else stock. Could it be possible that I need to move the clip on the needle and if so which way should I go? What will the BK mod do in this situation? It will be next weekend or the following week before I can try it out due to a bad lower shock bearing that I found tonight, any suggestion where I can find this bearing? Any one that has not check this bearing needs to, Yamaha does not put much greese in those parts at all. Thanks in advance.

Life it great until Ol Blue breaks

List you stock jetting.

clean the carb, change the plug, clean the air filter


1st find your correct main jet. WOT on 5th and see if how it feels (does it flat out), change a little in both directions 168-170-172? and see if better ot worse. if 168 is better then try 165 until its worse. Then try the same with the needle then the pilot. ACV must be disabled if you want to be sure about the symptoms you are getting.

Try a search for Jetting Qs, snap, more snap ... take a month off to read all the info :)

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