Thanks JD/Taffy


I think my my brain just overloaded but thank you for the enlightenment! First off I need to know what the term "tickover" is refering to and then I should be able to end my initial misunderstanding of how the needle works. Let me see if I understand now.The effective area of the needle can be broken into three parts.

1. The root diameter or straight area (top).

2. A transition area(from root dia. to the area of the needle that measures 2.515 dia)

3. The area that is the given taper(2.515 dia to the bottom of the needle).

Please tell me if this is correct.

By the way I read the article by burns again and I noticed he talked about not relying on the main jet by a good CO reading on an exhaust gas analizer(EGA), but could find no mention of not relying on a dyno for main jet tuning. (IMHO)If a bike on the dyno makes more HP and torque at wide open throttle roll on with say w/158 main than a stock 165 I would leave the 158 in and fly it. I think he is referring to the EGA.

Anybody think of opening up the bleed holes or adding more on the (crap) ET to see if this might help the air side. Seems like it might be a bit tricky and maybe not even worth the effort. Let me know....Woody


Taffy explained it correctly and I'll add a few comments and ideas.

-The first 2 letters EM are determining the angle and location of the taper, NOT the taper start. I am sure the needles are made in a batch. All EM- needles are made first with no straight diameter ground yet.

-The straight diameter is then ground on the needle and the last letter stamped (M,P,Q,R). The more material taken off makes the taper start lower. You can take an EMR and grind the straight portion down to make EMQ, P, N, M...

-Because of this, EMR and EMP will run exactly the same above 1/4 throttle for identical clip positions. Taffy's point is well taken.

-Below 1/4 throttle the straight diameter dominates. However, there is length involved in the ET and this is an extremely sensitive area. One needle clip position reduces the tapered portion by .017mm where EMN to EMR increases the straight by .02mm. You might not feel it on a dyno, but in real riding conditions a richer clip "somewhat" offsets a leaner straight diameter from 0-1/4 throttle. They aren't identical and it is a poor tradeoff to compensate for the wrong needle straight diameter but the clip is always used to correct for the straight diameters' mistakes. How do I know? I have EML, EMM, EMN, EMP, and EMR and the 2-stroke equivalents from a dozen dirt bikes of years past.

If you were thinking the ET has bleed holes, it does not. This is not an "air bleed" type ET.



if you have the 180 and 160 MAJ's you're welcome to join in! put your #200 back in and try it. it's the last few revs.

we're similar, you have a _ _P needle and 42PJ, i have a _ _M neeedle and 40PJ. your PS sems a little lean. maybe a 40PJ like hick needed at high elevation and PS back out to 1 1/2. then cut your APJ back even more.


WR timing has got me and i'm sure JD will help me by saying "in general" what happens to WR jetting.

no i haven't tried a more open pipe yet and it looks to be a month away. my Stroker tailpipe is for a larger bore header pipe than my Powerbomb and it leaked. i collected it yesterday with a nice aluminium sleeeve made by my engineer.

you say that your PAS is 1 3/4 but i think you meant your PS! the PAJ will be #100 (same as woodies?).

your MJ is low because you've been running a #200 MAJ which richens the last few revs by NOT introducing more air.

woody on the other hand is running lean (IMHO) at the highest revs so he put in a 168MJ. thing is woody is 10 too rich at max stomp in top (again IMHO).

again if you follow me- and don't forget WR v YZ timing, i'm lower on PJ at 40 and PAJ #85 and no APJ.

you've got the APJ and i've not run it for 7 months, racing and all!

i just think that a Q needle is too lean. JD likes an N or a P but as i live at see level i couldn't see any further than a M or N.

on sunday in my last test i put my EKP in for the first time for three weeks. and i had to kick 3 times to start it, i mean bloody hell! twice i can put up with you know, but...



didn't we used to be able to click on to a keihin chart for this?

you say that the needle straight is the main contributor up to 1/4 throttle, i would beg to differ. i think it helps a little up to say 1/8th throttle but after that the pilot takes over. if woody were to mark closed, 1/4, 1/2. 3/4 and WOT he would be amazed how quickly he was going at 1/8th!!!

you said that the clip is always used to compensate for the wrong needle straight and i'm sure you meant to say "but it shouldn't. the needle straight should be chosen correctly in the first place". correct JD?

the needle should be chosen for it's needle straight first, then what it can do for you at mid-revs which comes down to the clip position.

if anyone should talk about taper start it's me, as we both agree, having got the first two right the third (the taper start) is an elusive character that can't help but move up and down with the needle at this present time.

and if woody has been reading up, this is a project that i have been on about for 7 months! and is presently in hand.

if folks haven't spotted it i had my second ET drilled down from the top and it made no difference. i then had it reamed out from 2.9 to 2.95 mm on monday ready to be tried with the EKT needle. this will bring the taper start up 2mm whilst keeping the same 'gap' between needle and tube, however it is already expected to fail because i have already dropped the needle twice in the last month which is the 2mm i was struggling to get back; gone already.

next stage is that i have an EKX should have arrived yesterday and after JD's excellent maths, we know i need a 2.99mm ET. this will bring the needle taper start up a further 2mm making it 4mm in total.

however the needle is about 7/8mm down the ET so even now the results appear doubtful, but it's only when you arrive and try these things that you suddenly see new openings, so let's be optimistic.


hopefully JD can get you a keihin needle chart to click on to.

in the meantime you made one small error in your understanding of needles.

whichever angle a needle is ground at, it will be 2.515mm wide somewhere, ok? how far up or down the needle dictates it's middle letter.

that doesn't mean that they change the angle of grind at 2.515mm, ok?

a DBM and a DXM have the same grind but it's got cDeFgHjKlMnPqRsTuVw 10 clip positions to get there or .9 x 10 =9mm (that's a long way) the grind is identical but 9mm apart. this means the needle tip on DBM will be very thin and DXM -very fat, ok?


[This message has been edited by Taffy (edited October 10, 2001).]

Thanks guys, I do appreciate all the time you have taken to help my learning curve. I know you have been worn out with questioning on the whole carb/jetting subject.


I hope you don't mistake my analytical way of presenting an issue for distrust or unbelief in what you know. It is just a way of me better understanding an issue.

If you could please give me a brief discription of the ET on this carb. How does it make use of the air from the MAJ.

Taffy, I still need your definition of "tickover".

Dyno runs may start tonight if all goes well. Will be changing to the street tire on my lunch break and setting the bike upon the dyno. grin.gif

Woody meant to say "but it shouldn't. the needle straight should be chosen correctly in the first place". correct JD?

-Exactly Taffy!

I'm just used to seeing manufacturers pick the straight diameter rich on 2-strokes and lean on 4-strokes (except for DTM/DXM). 0-1/8 throttle is more noticeable for the needle straight, as you mentioned and I would aggree.


The MAJ provides air around the top of the nozzle, sort of as an air bypass to reduce vacuum. It doesn't feed the "emulsion tube" down at the middle like a few carbs do. Not sure what you're used to seeing. You can unscrew the ET and take a look at it.



Screwing with these air jets makes me wonder why they are used in the first place?

I grew up on two strokes hence my ignorance.

What would be the purpose of LOWERING the vacuum w/ the air jets?

I understand that by going smaller on the PAJ for example, you have to go in the fuel screw -Or- smaller on the MAJ means going smaller on the Main Jet...right?

If all this is true, it would seem to me this carb has a plethura of settings, as long as they all work together in harmony...right?

This article the Taffster keeps mentioning, Patric Burns is it, is it on a websight? If so, do you have the address?


'99 WZ/YR (you choose!) with ALL YZ mods, de-octopused, DSP Doug Henry airbox w/ velocity stack, FMF PowerBomb header, Stroker SX-1 silencer, SS front brake line, OEM YZ tank, IMS YZ seat, Mobil 1 15W-50.

NH Kevin,

here is a link to the web page


I am used to seeing air bleed ET's on Harley-Davidson's (Keihin butterfly and CV, S&S). i work at an H-D dealership. 12 years shocked.gif!


[This message has been edited by Woody426 (edited October 10, 2001).]

Well guys I've trudged through dyno hell. (two nights and 65 dyno pulls with so many MJ/MAJ combos I want to puke!)

I ran the bike starting at 4500 rpm in final gear and whacked the throttle WFO til 9500. The peak RW HP stayed between 44 and 45 @ 8100 rpm, while peak TQ was between 31 and 32 ft/lbs @ 7100 rpm no matter what I did.(within reason)Above is alt. corrected

Taffy,(while reading below remember @ 4600ft w AP off for accuracy)

I did find some truth to the "last few revs" theory of yours. I had run 165,168,170,172,175 with no MAJ. All curves overlapped tightly when stacked. 165 and 175 were getting rough an showing down on power a bit.(lean and rich ends)The middle three were good smooth curves. 170 and 172 had 1.5 to 2 more (approx.) HP between 8600 and 9500. Keep in mind that this is after peak where the curve on the graph just starts to go down. This same thing happened when I stuck the 200MAJ in with a 160 and 165 main.I did not have a 162 but it probobly would have been the best as the 160 was alittle short in HP (.5 approx) throughout. I tried a 220 MAJ but could not duplicate this little kick in the end rpm. A 220 produced its best curve w/170 main. It had a smoothcurve with a little more hp between 5k and 8k. At 168 it was almost the same and thats where I stayed. I dont have any leaner mains than 160 so I did not do any testing w/smaller MAJ's. I did try a 190 MAJ with a 160 and 165, but the curves were down so I stopped.

More info out of this to come but I will let you digest this first.


[This message has been edited by Woody426 (edited October 11, 2001).]

[This message has been edited by Woody426 (edited October 11, 2001).]


i don't think anyone answered your question about tickover-it's idle. bloody fools!

now there is no way i was going to explain that bonez so i'm glad you did! self explanatery i had thought.


there IS value to what you did and it's not always easy to see. but you have given yourself some parameters to work in. sometimes you sit there with a load of theories and they don't work and then one day you chase a rainbow and there is gold at the end.

you don't mention your initial MAJ? you say you go to 200 and 220 later.

if you are getting more power past the torque peak from having a richer MJ then a smaller MAJ will help. go buy a 180 and a 160 for example.

the MJ heavily undermines the needle IMHO so you will find that going up on the MJ will affect lower mid and ploughs through your clip settings.

what with the pilot circuit and the MJ, the needle really is the 'piggy-in-the-middle'.


It's there, No MAJ is where I started. Sorry I am so ignorant in my bloody english colloquialisms mate. smile.gif

Ta,ta for now off to have my morning tea and crumpets.

More later.


[This message has been edited by Woody426 (edited October 12, 2001).]

Is this with a stock US WR exhaust and baffle removed?

Did you alter the passage behind the main air jet? (enlarge it)

4500ft elev. and what temperature?

I read the results as: ***EMP needle #2 clip***

#200 main air jet- 162/165 main jets best

#220 main air jet(custom)- 168-170 best

Removed main air jet- 170-172 best




I did not alter the passage behind the MAJ, so according to what I have read and observed about 2.35mm.

The exhaust is stock with the black pinky hole baffle removed. Interestingly i made three runs with the whole end removed(three bolt end cap w/screen)and gained 3-4 HP and TQ between 4500-6500rpm. I'm in the process of making an adapter to fit 4" Supertrapp discs to the muffler with the stock end cap removed. I will make more dyno runs when this is complete. I need a little help fine tuning mine if you would be so kind. The bike does great everywhere except at constant throttle pos. between 1/4-3/4 (misses alot). I know that this is where the needle comes into play. I have moved the clip in 1,2,3.

3 was worst 1 and 2 feel the same. Do you think I need a needle that has the taper farther down since I have run out of clip?

A slight bit slow to come down to idle, but higher pilots make the 1/4 to 3/4 prob worse. Especially at 1/4 to1/2 throttle.

I am trying to comprehend all of this as fast and as best that I can but still a little foggy.

EMP#2, 168M, 220MAJ, 40 pilot, 5/8 PAS, 1-1/2 ps

Thank you for your on going patience.


[This message has been edited by Woody426 (edited October 12, 2001).]


HAH, The same problem I have! Whatever fixes yours will fix mine. I have the same problem with the EKQ.

Talking with Taffy, I am currently about to purchase the EKP. Unfortunately Sudco can't get the EKP.

Can someone provide me the Yamaha part number for the EKP? In light of Woodie's new information, are there any other recommendations? I'll buy a couple needles. Wish Sudco had them, Yamaha charges me $18 apiece!

I thank everyone for their patience as well!



01 WR426, uncorked stock pipe, sometimes Euro pipe, EKQ POS#3, #158 MJ, #42 PJ, 1 3/4 turns.


This problem of steady throttle sputter has been brought up by riders all over the world and continues occur regardless of jetting change. Both stock D-- and E-- needles and varied clip positions. confused.gif

By Comparison:

-The YZ426 uses EMP#5 1/2 (EJP#4) wich is far far richer without a significant problem.(I though it would be!)

-The YZ and WR250F use EMP#3 1/2-#4 1/2 (ELP#3-4), again without a problem.

-My previous '00WR400 used EMP#4 or 5(or EMN) the majority of the time with hardly a noteworthy sputter. Occasionally on a long downhill with high revs and throttle rolled off and on it would exhibit this. My suspicion was that either the accel pump nozzle or the deceleration bypass was richening the circuit from the higher vacuum and this could be an anomaly. If either circuit were blocked it might help identify the problem.

Maybe other riders don't notice it because they're always on or off the throttle.

The results are interesting Woody, tell us more! grin.gif


Sudco has EMP which is the same as EKP only 1 clip position leaner and made from brass($8).(EKP#3=EMP#4, EKP#4=EMP#5) You might also get EMN for a more smooth transition from idle to 1/8 throttle.



what did i tell ya. your 2 clips below the EKP recommend (as told) and more to come (as told).

i'm afraid we've GOT TO STOP RECOMMENDING the old settings. i couldn't be clearer now could i!!!!


go to EMP clip 1

go to 200 MAJ

go to 165/162 MJ

PAS out to 3/4

APJ off (yes really)

PS 1-2 (test)

your MAJ is the wrong one. when you get the 180/160 it'll be better and you can come down on the MJ to 162/160. this in turn (as told) will lean off the midrange by the equivelant of 1/2 a clip. the fact that you've come down from clip 2 to EMP 1 means a kind of 1.5 clip drop.

welcome to the 40PJ club!

your next needle should be an ERM or a ERN and i would go for the ERN because the smaller the pilot the quicker she'll go.

your about 7 days behind me at this stage. i've found out that the smallest PJ is a 35.

the problem all along with this bike has been that when the jetting is good-no problems.

when the jetting is slightly rich you get a misfire.

but when it's quite rich it runs ok again.

recommend you buy the ERM, ERN. a 38PJ and 180/170/160MAJ's. 160/158MJ.

while you're there i would run a '9' plug now that your settings like mine, are finally after 4 years of this model COMING DOWN TO THEIR CORRECT SETTINGS.

woody i could bloody kiss ya!

stefe, get out there and do it. i don't remember recommending you get an EKP. i thought you had one already and was asking you to put it back in. i think you gotta get off your bum and go to work. the settings i truly recommend are the one's i have on "jetting Q's" and i've even forecast my next move.

as good as it is on this post, some of you will do well to follow the long hard slog over this past month to get to here so that Woody has got this guidance.

there are dozens of owners who have had their bikes done on a dyno. the dyno guys never helped them! if they did we've never been told have we! and when the owners got the info did they tell us?



[This message has been edited by Taffy (edited October 12, 2001).]

[This message has been edited by Taffy (edited October 13, 2001).]

Funny how you made mention of this "deceleration valve". I am going to assume that this lets air in during decel.

I am looking in the factory service manual at a chart that shows how all the circuits effect different throttle pos. On this chart is a "throttle valve cutaway circuit." It show it effects idle to 5/8 throttle. It makes no other mention of this through the entire manual! What is this, is it the same as your decel valve? But why would show it has an effect on the circuits?...Hmmmm

Did the gen 1 FCR have this? (98-99)

I have two Rotax dirt bikes at the shop that have FCR slant 41mm from Sudco. Both are jetted close to mine, and they scream, have great start up, decel and steady speed etc.

Both have EMR #2????????????????

Tell me more of this decel valve JD.



I am not JD, but unless I am sadly mistaken, the cutaway is the "notch" cut in the bottom of the slide valve. With the throttle closed, the notch allows air flow through the carb (from the airbox).


'99 WZ/YR (you choose!) with ALL YZ mods, de-octopused, DSP Doug Henry airbox w/ velocity stack, FMF PowerBomb header, Stroker SX-1 silencer, SS front brake line, OEM YZ tank, IMS YZ seat, Mobil 1 15W-50.


Kevin is right, the manual is referring to slide cutaway. This is not what I was suggesting.

There is a diaphram on the side of the carb which is supposed to operate under deceleration from the little I've read. There really isn't enough information about it to draw any conclusions either way. I would also suspect extra air rather than fuel would be drawn through the circuit. The YZ's don't have it and your Rotax machines probably don't either. The 1st generation WR carb's had the "octopus" hoses instead.

The latest news on the CRF450 is that it has an needle EKR#4 (EMR#5) which falls right in line with the other YZ settings. I know my WR was weak and unresponsive at clip #3 while using a YZ silencer. It would bog more easily unless at clip #4-5. So the exhaust systems are a factor in what settings will work best. A big carb with restrictive exhaust are at odds with each other. KTM's use leaner clip positions with the quiet S/A's and richer ones with SX mufflers. These are things to consider when taking suggestions on how to jet your bike. Use your own judgement and compare the settings yourself.


(Woody, what's your email?)

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