jd jetting (fouling problem)

I installed blue needle clip 4, rest of carb stock. Took bike out and fouled plug in 5 minutes. Temp was maybe high 70's, but humid, ride in michigan around 1000ft. So I'm guessing that I need to try the red needle clip 4. Could there be another problem why I am fouling plugs. I think I might try to put the eln clip #3 needle back in to see if it still fouls so quick.

Tctrailrider if your out there,

I can't understand if setup works for you and your in Traverse City area, and it won't work for me and I'm in Gaylord. Thats why I'm starting to wonder if there's something else going on. (My air jets were not clogged from the air cleaner foam oil).

The first thing you should try is new gas, from another source.

That should not happen from the jet kit alone. The needle you ran has the same diameter as the ELN you were running before.

-Did you turn the fuel screw out from where you were before? Go back to your previous fuel screw setting, or turn it inwards 1/4 turn.

-Anything else changed?

The kit has very specific instructions based on testing and setup with both stock and modified WR's. If you have altered the other jets, then the settings can be off. For example a larger pilot jet or disconnecting the ACV will have the fuel screw too rich. The YZ has a bigger(#100) pilot airjet than the WR, so settings on the fuel screw or pilot jet are not the same.

The next step leaner would be to use the blue needle clip position #3(3rd position counting from top), then the red needle #4(middle position).

Be sure to recheck the fuel screw setting.

What fuel screw setting and main jet were you running before?



Thanks for responding. Before I switched to your jetting, I was running eln#3, 165mj, and was trying different pj/paj combos, with 200maj. I had a studder that I was trying to get rid of in first and second gear as the rpms started to build. I also installed zip-ty pas screw the last time I rode my bike with eln in it. This last time out with JD setting was all stock except blue needle on #4, pas was 1.5. I didn't get a chance to try different PAS settings because it fouled out so quick. When pluged fouled the bike died and would not start for a little while. When I got the bike started it was backfiring and barely running, so I pulled the hot start button out and the back firing stopped and ran a little better enough to get home. If that means anything or helps. I wont get up north again for a couple of weeks to try out your recomendation. Actually now that I think about it, when I had my eln needle in, my zp-ty pas was not all the way in, you would be looking at the 3 when I thought I had it all the way in, however now the number 1 faces out at you when screw is all the way in.


I put in another 60 miles of single track this weekend, and the bike is running great. I tried the 38PJ and 65PAS and it seems to lug better, all else the same. Per an earlier reply is your gas old? Before you fouled the plug how did it run, low, mid and WOT? You mentioned a Zip Ty PAS at 1.5, do you mean fuel screw, on the bottom of the carb?

Stock PJ is 42 with 75PAJ. Are you running 75PAJ or do you have the adjustable PAS, if so how far out from all in are you? The PJ or PAS are on the air boot side of the carb, you need to take off the black plactic bell to get to them.

I think its your gas or the pilot circuit. Pull your fuel screw out and check to see if the tip looks OK, I have heard of them breaking off.

My gas was brand new from the pump. The 1.5 is the ps, I took out the pas when I went to jd jetting and put back the 75 paj. I'll pull out the zp-ty ps and make sure the tip is still there. Depending on wheather conditions next time up north, I might try the red needle #4 with everything else stock just to see what happens. It fouls out so quick that I figure one clip up on my blue needle probably wont be enough to get it running right if thats the problem.

165 main red #4 and stock pilot should work very well for an uncorked 426. Replace your spark plug as well. You will be amazed. :)


It seems odd that you would have a problem with the setting that I tested and so many other riders use with great success, and have been getting positive feedback on for months. This has been from sea level to 5000ft elevation on clip position #4 with exellent performance.

I aggree with the suggestion though, try the red needle in clip position #4.

Keep the Blue needle #3 as a potential setting because the jetting is mostly leaner than where you started with OBELN#3. It transitions leaner/richer/leaner when using the triple taper needle.

Check the carb over carefully, making sure the fuel screw spring/washer/O-ring are in place. Chacke the airjet passages by blowing air through them and the pilot (fuel) jet is clean.


Thanks for the help. This weekend I am going up north to work on bike. I will try what you suggested, red #4 and blue #3. I can't understand either why I am having a plug fouling situation riding in Michigan with blue#4 rest stock, when others in Michigan are not. I may have another problem to deal with. If I put in red #4 with rest stock and it still fouls then I know forsure the problem is else where.


I got bored so I put in the Red 5 to see how is was. Had the 38PJ in so I left it. Ran good on the way up but some severe bangs on decel. Put in 42PJ and 75PAJ, bangs were gone. Running very strong. Its about 80 today. 2nd gear on pavement I had to roll it on slow to keep from going over backwards. Its close but Red 5 seems a little better than Blue 4 at this temp.. Not sure why you are fouling plugs. I think you should dissasemble, carb cleaner, and air compressor your carb. Make sure there are no air leaks. Red 5 or Blue 4, all else stock and you should be rippin.

check the fuel screw spring/washer/O-ring

These parts are VERY SMALL. When you pull out the fuel screw, the parts that may/may not come out are (in order):

1 - spring

2 - washer

3 - o-ring

it is quite common for any of these to be stuck in the carb. Last time I disassembled my carb, I lost the o-ring and have zero clue how. After that, my bike backfired constantly (sucking air).


The red needle #5 is another setting that can be great! The warmer temperatures is usually what sways me to run it. Good suggestions.


I just came back from a weekend upnorth trying to get my jetting right. The first thing I did was unscrew the zp-ty ps to see if tip was broke or missing washer, o ring, or spring. Everything was there when I pulled it out, and tip was ok. Next I put in new plug with:

- red needle at #4 with rest stk. The bike had no cutting out or poping/backfiring, but it felt kind of weak. I pulled the plug after short ride and the tip kind of looked white so I figured I was to lean.

- next red #5, rest stk. Seemed a little better but just didn't have that arm ripping power. I pulled plug after ride and tip of plug still a little white.

- next I went to blue #3 with 168mj, rest stk. Better but just not right. With eln needle, 3rd 4th and 5th gear just felt so much faster.

- Last I tried blue #4 again with all stk. It ran pretty good. I can't figure out why the last time I was upnorth it fouled out right away with this setup. I pulled plug after ride and it was however pretty black with soot.

My question is when I go up say to clip #3 blue, should I raise the mj at the same time. Also when I had the Blue#4 in, I could kill my bike by turing in ps all the way, so I'm assuming I can't go any smaller with pj. The temp was mid 80's and humid when I was doing the jetting. Next time up I plan on keeping the setup I have blue #4 and see if it still runs good, or if plug will foul. Maybe I'll try different mj's to see reaction of bike with this needle and clip#4 in it.

What is a healthy spark plug suppose to look like in one of these bikes. My last bike a dr350, the plug was always tan, no black anywhere. With this bike, every time I have looked at the plug it has been always black around the circle, with tip varying, but usually black. Not wet, just alot of soot.

Just make sure you didn't put the carb slide in backwards this seems to be happening a lot, I know 2 people that did this, because it looks like it goes the other way.

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