Jetting is real close, but not perfect! HELP!


I have recently switch my 02WR426 to YZ timing and YZ exhaust. I am running an EKN needle in 4th clip, 160MJ, 160 MAJ, 38PJ, 65PAJ and fuel screw at 1.5 turns out! The bike rips once opened up, but when cruising at a steady pace it wants to hesitate and has minor popping. It does not sound like it is running smoothly and you can feel the hesitation come on and off. I do not really notice it on the trails, except real low rpms. I mainly notice it when I jump on the road coming home! It is most noticeable at roughly one third to half throttle. Do I need to raise the needle one clip? :D:D

For the popping try 40 PJ and 85 PAJ(s) - hope you have the sudco screw PAJ. fyi, I personally liked the 180 MAJ instead of the 160 MAJ. It gave me more top end pull with the YZ timing. I may even go back to the 200 MAJ, I have a feeling it maybe even better on the top end for the yz timing. The bigger MAJ allows more air (and fuel) to get in at the top RPMs. For the hesitation, you probably have to lower the needle to clip 3, not raise it.

I suspect you are running rich on your needle (If lowering this needle to clip 3 does not do it the try this) Hesitation and a deep sputtering sound when backing off the throttle from constant throttle position is associated with being to rich. EKN needle may be too rich a taper or diameter or both. I would put marks on a strip of duct tape next to the throttle and see at what opening at constant speed do you really notice the hesitation. If at quarter throttle then the diameter "N" is to small and maybe you need to try a "P" needle. If it is at half throttle then I suspect it is your taper "K" needs to be leaner so you can try "M" taper needle since "L" may be hard to find. If it is at 3/4 throttle and full throttle you need to go to a smaller main but I doubt you are rich on the main. Try an EMN , EMM or EMP needle from Sudco. I have tried all of them. They seem to work well on the WR uncorked in cooler weather. :)

Thanks for the help guys! I am going to try lowering the needle one clip position as recommended in this post to see if the slight hesitation goes away. As I mentioned before, my bike rips on top end. I am wondering if the James Dean Jet Kit would make my bike even better than getting it dialed in with my current jetting stated in my signature! Can anyone that has the James Dean kit elaborate on the performance gains over trail and error "ball park" jetting?

The JD needles are different. The Blue needle is a "M" diameter with a triple taper, The Red needle is a "P" diameter. Both are leaner than yours above 1/2 throttle but the Blue is slightly richer at 1/4 throttle as your needle and the red is leaner at 1/4 throttle. So I would say try the JD Blue needle to lean out you 1/2 throttle and up range. The JD tapers will suit your bike but the blue needle may be too lean in the winter for you. :)

OK, I tried dropping the needle one clip and it made the problem a little worse. Also, it seems to have more hesitation around 1/8 throttle so that is telling me that I have to make a change to my pilot circuit. The question is to what should I change?

That sounds weird. Just to make sure, with the needle out of the carb and the pointed side pointing to the floor, moving the needle down means moving the clip from the 4 slot from the top to the third slot from the top. This makes the transition leaner. Is this what you did? If so, then, maybe you need to go the other way, richer on the transition. :)

Yes, I moved the clip up to lower the needle! My next experiment was going to be raising the needle one clip from original (4th) to see what it does. I am still wondering about the pilot though!

I tried moving the needle up one position from original and it was worse yet. The clip in the 4th position was the smoothest, so I must have to change my pilot. I am going to mess with the fuel screw!

I moved the needle back to the 4th position, and it is much better than the 3rd or 5th position. When I use the hotstart the problem almost goes away. So based on the info given to me, I was told that was a rich condition. If I turn the fuel screw into like .5 turns, it should run better, correct? Man this trial and error stuff sucks!


Sounds like your getting to know your carb.. Earlier this year I embarked on a jetting Quest. Did several tests with MJ from 155 to 175, PJ 35 to 48, EKN, EMM, EMP needles. I ended up at EMP3, 38PJ, 160MJ. When I tested the EKN clip 5 was good. Clip 4 and 3 were terrible but clip 2 was the best on that needle. That is not a typo, clip 5 or 2 were good and in between was terrible, as to why I have no clue. Didn't count but I must have tried 50+ combo's, ended up very happy with the results. Ordered the JD kit because I like to tinker. Returned it to all stock jetting with the Blue needle on 4 and everything was great. In the heat the Red 5 seems better. Either needle is very strong, no pops or bangs, starts great hot or cold, fuel screw 1.5. I will run Blue 4, temps 70 or under, Red 5, 70 or over. I can only speak for myself but first try with the JD kit was as good as 50 attempts with the E taper needle. Have fun.

Hey Eagle, I have been saying all along that the WR's seem sensitive to needle length and clip position 4 and 5 work best on any needle. That is why I recommended trying a different needle. You can logically improve your needle by knowing where it is lean or rich along its useful range. Try JD Red 5 or JD blue 4 :)

Dang it! Dang it! Dang it! I was hoping to get the jetting real close because I am leaving on Monday for a 4 day riding expedition. I am going to give the James Dean kit a try when I get back. I tried turning in the fuel screw to like .5 turns and it hesitated and ran like doggy doo clear up thru the throttle range! I have had the carb off and cleaned and checked for air leaks, but have not noticed anything out of the ordinary! I put the needle back on clip 4 and fuel screw back at 1.5 turns and the hesitation is from 1/4 to 1/2 throttle. I placed tape around the throttle grip and markd spots at Idle, 1/4, 1/2, 3/4, and WFO! Does anyone have any other suggestions?

1/4 to 1/2 throttle is your needle diameter's main effect. You have to get a new needle. There is no other solution except to cork it back up. :)


Try clip 2, that was my best setup with the EKN.

With EKN#4, try turning the fuel screw outwards in 1/2 turn increments and give it a test ride. Go out as far as 3 turns.

Try a #40 or 42 pilot jet with your #65 PAJ to see if the lag is lean.

The small PJ/PAJ combinations were developed by Taffy using an EKM#4 (EMM#5) needle setting. This is richer on the diameter or in the 0-3/8 throttle range and where you are looking at. He also had no "Air cut valve".

As you go to a bigger pilot jet, the fuel screw can be turned closer to 1-1 1/2 turns to keep the idle clean running and have it richen at 1/8-1/4 throttle. For example, a #42PJ/#65PAJ and 1 turn out may be what you're searching for with EKN#3-#4.


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