Another Stupid Jetting Question...

OK, I know you're all sick of these jetting questions. BUT! I've got a 2000 WR400. It's got the airbox lid removed, throttle stop cut to 24mm, grey wire disconnected, YZ timed, and a Thunder Alley pipe on the end of an 2002 YZ header. I live and ride at an elevation of 4500+ ft. Here's how the jetting is set up:

Main Jet = #170

Pilot Jet = #48

Jet Needle = standard OBDRS, #2 clip position

Pilot Screw = 1 1/2 turns out

Recently I've been adding octane booster to my 91 octane pump gas. I do this cuz I've been told that it should help in reducing the plug fouling problems I've been having. Get about 6 - 10 rides on a plug before it's useless. Kinda wondering if this may be hurting the jettin too.

Here's my problem. Now that it's gotten a bit cooler, 50 degrees instead of 75+, it's just not running right. It's popping & hesitating around 1/2 throttle. Nothing wrong at all down low or WFO. Just in the middle. Tight single track stuff is just killing me. It's not backfiring just a popping and coughing kinda thing. According to the manual, I should just lean the needle a bit. But cooler temps would normally mean I'd have to richen the mix not lean it. Right?

I'm thinking that I probably need a new needle. But which one? I've seen alot of people using E series needles. But again, which one? Anyone know what works good at my elevation? Which clip position? :D :D :)

Any help would be appreciated.

My 2000 Wr is doing the same thing.

See my post on 200 Wr jetting right next to yours.

I Bk'ed and am going with an EJP/EJN needle when they arrive. Seems like you are in the same boat as me.

Mine is a little flat on top too, but I run a 165 stock MJ.

I ride a sea level 30-40 deg lately and getting worse with the cold.

Colder weather will make the bike run LEAN

Higher altitude will make it run RICH.

I guess yr 170 MJ is okay and yr needle is Lean especially on clip 2. (I'm on 3) Raise the needle 1-2 and see if helps.

Let me know, as I am considering doing the same while I wait for the "E" needles. I'll let you know how the "E" needle works.

My bike has a YZ can which made the lean condition worse.


The both of you are running about the same altitude as I do. Steve what PAJ are you running with that 48 PJ? If you have removed the Air Cut Valve (ACV)...Which you should...You can run a summer jet setting 60 deg or > or a winter setup of < 60 Deg....Below is the jetting I run in both my YZ and My WR for each season....Altitude is from 0-5000ft

Summer: 170 MJ / 200 MAJ

48 PJ / 100 PAJ

65 SJ (Choke)

FS 1 1/4 Turns out

Winter: 168 MJ / 200 PAJ

45 PJ / 75 PAJ

60 SJ

FS 1 Turn Out.

I also run WB E-Series Exhausts on both bikes (OPEN) You can go leaner on the pilot to lets say a 42 or a 40 with the 75 PAJ. The main rule of thumb when playing with the jetting is that you must match the proper PAJ with the correct Pilot...If you don't...Lets say that you run a 48 pilot with the 75 PAJ....Your going to be off balance and will foul plugs constantly.

Do a search on "Jetting Q's" there is a monster thread that explains in detail of what works and what doesn't.....JD's Jetting Guide is also a great work that he put together over the course of a year or so and is a great tool to have....It's for sale at the TT store and worth every penny.

Good Luck...

Bonzai :)

look up jetting Qs without the apostrophy i'm told is the way to go?

i see yamakazi that you go leaner in the winter. that makes the riders who go leaner in the winter now up to er! two yep me and you mate!!

i never did win the battle over air density and i guess i never will so like you all i can say is "jet leaner in the winter folks" and asked why i'll stick to dunno from now on.

you two lads at the top are running so rich that rather like a gasping swimmer coming up for the third time you've had it and your bikes are spluttering.

go with the 75PAJ and 40PJ and your MJ can be about 165.

the DRS or whatever needle is awful so go for something like a D*N for smooth power or the E needles one of you already mentions for rip-roaring success.



DRS needle



or go the whole hog like jetting Qs says.


Look at Motomans site, jetting for the 01 YZ 426. There are charts for the different jets and shows the effects of altitude and temperature. I have the 2000 WR 400 that has the same carb. as the 01 YZ. My thoughts are that if I jet a little leaner than the YZ it should be OK. I went to the OBELN needle and found that I needed to go smaller on the main, from 170 to 165. When it warms up I think the 160 will be good. The E needle will be richer, low and middle and may stop the popping. My experience is that the main has an effect on much more that top end. I was half way through rejetting and then the snow came, so its a work in progress. The 99 and older WR had a different carb, and the Euro models are different. My theory is that the 2000 and newer WR and YZ, US models have the same carb., so the closer you make your WR to a YZ with all the mods, the closer the jetting will become. You will like the E needle.

Well I think I'll try one of the E needles and see how it works. Anyone have suggestions for someone at my elevation? 4500+ ft, spend quite a bit of time at 6000+. ELN maybe? Most of the jetting suggestions focus on mains and pilots which I'll change to the leaner 165mj, 200maj, 45pj, 75paj, just looking for more info on which E.. needle works at what elevation.

Thanks a ton for your help guys!!!

Man I'm really confused.

I thought the bike would run LEANER in the winter???

And leaner with a YZ can. It's even starting to backfire.

Don't tell me my whole approach and advise to this gent is WRONG!!

My Jetting is STOCK US WR2000.

I presume it has a 165 main and a 42pj 75paj.

Is that correct, or must I buy a PAJ too?


You will run leaner in the winter and leaner with YZ can, and those are the stock WR jettings. Leaner conditions require larger jetting. Backfiring is a lean condition and I would guess you need to go down a clip and or try a larger PAJ. I see a lot of posts with leaner than stock settings on the WR and this is after the mods that increase performance. Seems like jetting should get richer. I think the stock WR is a pig and using the stock jetting as a baseline will get you into trouble. Search under jetting Qs on old posts and there is a ton of great info there.

I would also highly recommend the OBEKN needle on the 3rd clip, if you want explosive low and mid range power. I had to tame my WR and YZ a bit by adding a 10oz Flywheel weight to both....They would constantly break traction with a slight twist of the throttle. Still monster power, but much more control.

Bonzai :)


EJN and EJP needles are on the way. I presume they are 1/2 clip leaner than a EK series, no?

I Bk'ed already, Beyond that what other jetting changes do you suggest? My pilot might be okay as the bike starts first kick all the time. Always has.

Mind you I'm WR timed, lid off, stop trimmed, and yz can'ed.


1/2 to a full clip atleast.....Running a leaner needle, you could very well get away with Taffy's jetting, and be running strong still. I tried the EJ series needles but found with the winter temp swings that we get here in Georgia that I was getting a little too lean when the temps wer up above 65 deg or so. You might be ok, as each one of these bikes acts just slightly different. If you find yourself chasing the fuel screw everytime the temps change you can always go with an EKN later's only 12 bucks retail from Yamaha...not a bank breaker. The one thing that you really need to be sure of is your PJ/PAJ ratios.....Remember that you have to be balanced or your either going to be too lean or too rich (38/40/42/52 Pilots go with a 75 PAJ) (55/58/60/62 PJ's go with a 100 PAJ) If you use a 100 PAJ with any of the 1st set your going to be too lean.....a 75 used with the second set will be too rich. I don't know how many carbs I have opened in the past three years to find mismatched jetting from the factory.

Jetting is really easy if you follow a couple of simple rules.....(DECELL POPPING) Before breaking open the carb, attempt to remedy with the Fuel Screw (FS), If you have to open more than 2 full turns from fully closed, your pilot is either too lean or your needle is too low....(Check the needle position and verify that the PJ/PAJ balance is correct) If adjusting the needle does not produce the desired result then go up one size on the PJ until you can adjust the FS from 1/4 to 1 1/4 turns with no more popping. If you are getting 3/4 to full throttle hesitation do the same thing with the MJ, I have seen MJ's come from the factory from 168 to 175.....The 200 MAJ works well within this range, but I have found that in my area a 170 works well in summer and a 168 in the winter without having to change Needle clip positions or the MAJ. Again, Taffy's leaner settings work well in some bikes as well.

In Short, the important thing is to ensure that the carb is balanced, Once you get it that way for your area you will be good for a wide range of elevations.

Good Luck....

Bonzai :)

Backfiring is a lean condition

It has been my experience that backfiring can be caused by a lean or a rich condition. It depends on the sound of the backfire. If it sounds higher pitched and more like a crack, then it is a lean condition. If it sounds lower pitched and hollow or throaty, then it is a rich condition.

As for jetting in Cold vs Hot temperatures...well lets not start that debate. I just know that I had to richen my jetting slightly when the temp dropped.

Motomans jetting guide richens jetting as temp. drops. Yourself, Yamakaze, and Taffy go leaner. Whats a guy to do. I'm sure you know what your talking about, and I know the other three do, and I know I don't, I find a winner and copy it. Now my winners disagree on something that should be science. The jetting ussue has been making alot of sense to me and then Bam. Think I have to flip a coin.

Just to clarify, I think you should richen (mainly by raising the needle) as the temp drops. Good luck with the jetting, I think your on the right track. Jetting is a science but there are so many variables in it that it turns out that it's an opinion. :)


I completly understand your confusion pertaining to these jetting recommendations....If you knew how many hours I spent in a controlled disagreement (discussion) with Taffy and JD my first winter with my WR you would be astounded. My problem was that coming from a automotive background building carbs, these recommendations went against everything I was ever taught in school or in the shop. I was kind of hard headed (as Taffy will attest) and spent a month going in the oppisite direction and wasting alot of money on jets and needles (Remind me to show you my collection sometime) Out of pure frustration and a lead copy of JD's jetting guide (Thanks JD) I began to see how bringing the Pilot Jet down with the corrusponding Pilot Air Jet brought the carb into a flow balance. In my case the EKN needle was perfect because it slightly richens the circuit but does not screw up the mixture entering the combustion chamber at the low and mid range. Since the Main at 170 was causing a bit of hesitation in temps under 55 or so degrees (Rich Condition) it made perfect sense to drop the main atleast 1 step to a 168, and this as JD had professed cleared up the 3/4 to full throttle hesitation in the cold. We did lots of testing with the EKN needle at different positions.....It was a snap wheelie monster on the 4th clip position, but was really fat when it transitioned off the pilot and onto the main. The 5th Clip position just sputtered and shook all over the place. The first and second clips were way too lean. Taffy went one step further and lowered both the main and the main air jet until the lower needle clips could be used to produce really hard hitting power without leaning to the point of pre-detonation......I could not get my WR to respond the same way...too many variables to pin down the problem precisely. But to make a long story short, the leaner settings in lower temps work as JD and Taffy had preached. I have re-jetted between 40 and 50 bikes of all makes and models in my geographic area with the same results. Just fininshed my second YZ450F last Sat with really great results.....Expert Rider happy = Success. In my case I should have listened to JD and Taffy much earlier than I first did....I could have saved about $100.00 in jets that sit in little plastic cases in my tool box......

But that's just me.

Bonzai :)

I truly think I'm a little lean

My noise on decel is "popping".

I'm familiar with the "bang" backfire you get when you leave the choke on too long or start a loaded up motor and this is not that. I'm already on 2 turns out on the FS so I very well may need a 45 pilot. I will look to make sure the PAJ is a 75 (If I can find where it is)!

The mid range feels flat on power, not shuddering and breaking up but rather like when the bike goes flat if you ride off with the gas off. I turn the throttle slowly and it just don't go anywhere. Much more pronounced with the YZ can, runs better with the WR can and Vortip.

I think I'm in the right direction goig richer but do you think I can just drop in a EJP and be okay or should I use a DTM and just try to get an EKP and a new MAJ and install them as a set?

Lastly, can anyone advise exactly where I can get these jets and needles as well as the recommended assortment of what I will need to begin to play in earnest. My Local guy and Sudco told me they can't get an EKP needle.


Your local guy can get the EKP

Here is the Yamaha PN for the EKP needle:


Just give the parts guy that number and ignore whatever he says he thinks it is. It is an EKP needle off the '00 YZF fiche, no doubt about it.

Or you can order them online, the drawback with that is you don't have someone on the other end to tell you if the part is on backorder.

HLSM '00 YZF Carburetor Fiche

If you note the above URL you may discover the source of your local parts guy's confusion. The EK* needles are all listed as EV* needles, this is just a typo of some kind, that PN will get you an EKP.

Of course it should be much easier to order the standard '01 needle, EJP, vs. trying to hold your parts guy's hand to find an optional '00 needle.

Here is the EJP PN:


HLSM '01 YZF Carburetor Fiche

The only diff EJP vs. EKP is the former is 1/2 clip richer, so you should be more or less indifferent between the two.

Also, the PAJ is behind the black plastic carb bell at the back of the carb, it comes off with two 6 mm allen head bolts, there is a shaped o-ring between this part and the carb, there is also a slot in the plastic bell that allows some access to the air jets, but it is probably easier to just remove the bell. If I remember correctly the PAJ is on the left, MAJ on the right. Easy enough to check, the MAJ will be stamped 200, PAJ 75 on a WR.

Hope this helps.

Man, you guys are great.

You're right, the parts guy told me all he had was a J and a "V". I certainly didn't want the "V".

Thanks a million. I know I'm in good hands with you guys.

Now if my wife will let me sneak out to the garage...

Thanks again


if you've read jetting Qs-and yes it is hard work-you'll notice that we were always going the wrong way with the jetting!

one thread nobody asks to see is the MAJ tests done by "andy from australia". everyone was drilling out their MAJ including me!

all beca\use patrick burns said do and we all thought it was a good idea.

it was only when i did a day of testing and got chased out of the forest by the game keeper that i said "wow! it's the OTHER way". my point is, nobody, that's NOBODY has been totally clear about rich from lean! the only way to test was to test back-to-back and to trust your senses.

#45 is the wrong way to go, some riders get in a jam as they come down; weaning themselves off the rich factory settings, only to get a cough or a splutter that they immediately bottle it over.

it usually happens at #42PJ. if you're doing sound B2B testing you'll end up with similar jetting to mine.

depends how hard you're prepared to try.



Thanks for taking the time to respond.

I know you must have better things to do, like ride.


My plan of action is to leave the stock jets in and pop in a EJN 3rd and see what happens. I'll play with the screw a little and move the main around as needed. My Wr is street legal so I should be able to test it. Really, all I want to do is get the bike running hard with the YZ can like it was with the WR can in the summer.

It's snowing like crazy right now but I will buy the air, main and pilot jets as per your specs and give it a try when the weather clears up.

I figure no sense fine tuning the jetting in the middle of a snow drift anyway.

If the E needle and the BK mod bring back the snap the bike had with a reduction in AP bog and stall, I'll be happy.

Of course, if the bike starts to foul plugs or won't start then I "have to go Taffy early"

BTW, I've had the same plug in the bike for a full year.

Bike was "new" when I got it.

Never got the factory plug wrench w'the bike.

Any tricks to pulling the plug with a normal socket wrench or must I find and buy the stock plug wrench? Anyone got a part no?


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