Jetting EKP vs DVP

Thanks Clark,

- made a copy for my records.

My current setup is:

YZ cam timing

'99 YZ exhaust

air box cover off

stock filter


PJ = 48

Pilot Air = 100

EMP needle #4 (modified to triple taper)

Fuel screw = 3/4

Main jet = 168

(note that my needle is effectively 1 clip richer than Clark's, EKP#2=EMP#3)

This setup has no weaknesses from my perspective. It has not been tested much at WOT to know whether it could be better. The back end will break loose quickly with too much throttle, landed me on the ground today pointing the other way. It forces me to use more throttle control and stay in higher gears than my CR250 did. More like the well jetted KX500's I've had.

Clark, Sudco told me they don't have an EMQ, are you getting the EVQ?? I will also be getting more needles to modify, EMN,EMP, and EMR. They are due here Wed.

James Dean

For the record my 99 WR bike is set up as follows:

YZ CAM timing

Final drive 14/47 6% taller than stock

Vortex Dual curve ignition

DSP CF Complete air box

FMF PowerBomb header

Stroker Sx-1 SA exhaust

White Brothers power filters

Wiesco 420 kit at 13.5 to 1 compression

Works Racing CNC porting

Outside air temperature 70 to 90 deg F. Altitude 1200 to 2800 feet.

Its taken me a while to post this as a lot of testing needed to get accomplished five days over two weekends.

After a couple of disappointing 2 hour test sessions with the EKP needle I got my bike running basically ok with jetting as below:


EKP needle #2

Fuel Screw = 1.5

Main jet = 165

Top Speed Achieve 91 mph

The main jet needs to be run much leaner and the bike will be more responsive to main jet changes as the needle diameter throughout the tapered section is smaller than the "D" series needles. I would estimate the range of main jets to be 158 to 170 depending on altitude and air oxygen content. Most likly range 162 to 168.

With the above jetting and several variation thereof, I still could not get rid of a momentary stumble while transitioning onto the taper. In third gear while trying to hold a steady speed (28 to 35) on a small incline it would stumble same in 4 and 5 just at different speeds. If you flash through the gears it will ride through it and its not as noticable. However, if you dual sport or ride at a reasonalbe pace on trails it can irritate you. I know I can jet this out but no success yet and it may take a custom taper needle. I think the EKP is coming on the taper too soon for the 400.

I have ordered from Sudco a EMP, EMQ, and a EVP for evaluation. I believe the EMP being 1 clip leaner than the EKP will be a better fit. I will also test the EVP (which is 5 clips leaner then the EKP) and may make a custom taper on this needle to smooth the transition from the straight section to the 1 degree tapered section. My gut feel is this is where the payoff will be.

As far as power I think EKP has more mid range snap or pull but it may be my imagination as I can snap the same wheelies in the same gears at the same speed with the DVP needle more to follow.

I ran the same course, my standated evaluation course 52 miles, with no other changes except with the following jetting:

PJ = 50

DVP needle #4

fuel Screw = 0.75

Main jet = 178

Max top speed 94mph--Always evaluated on the same section of my test course.

This jetting is smoother top to bottom there are no stumbling, serging or hesitation spots. On the hard pack dirt road section covered with gravel and loose dirt I had better traction control and could ride faster. The EKP with the jetting described tended to break the rear wheel lose easier maybe better for motocross.

I feel that today if I was not a tinkering kind of guy and just wanted to go ride I would stick with the DVP, remember I dual sport and trail ride and do not motocross.

However, I will continue testing the "E" series needles until I can get rid of the serging/hesitation and if I can then maybe I will have a smoothe more responsive power band--but I'm not there yet. More testing to be accomplished and results to be posted in the future.

Any others out there in forum land running these needles please post you observations as they will help speed closure on a final "E" series jetting setup.

And the beat goes on


James Dean

I believe the transistion stumble is related to my Vortex ignition. I had to work with the jetting after installation of the Vortex to get a similar hesitation out with the "D" series needles. I feel after further experimentaion I will get it working with the "E" series. Havent got there yet.

Thanks for all of your info and insight



How do you do the mod to a tripple taper. I usualy use a dill press and polishing paper but control of the actual final profile is a little shaky. I mark the area to be modified with a marksalot and polish off the marking then test and try it again. I'm not a machinist and this is really whats needed as my experience has shown that the bikes are responsive to very minor variations in taper, so its easy to toast a good needle.


Clark- Thanks for sharing your results. I'm still considering the EKP, would like a little more punch. But I'm not a tinkering kind of guy (to use your words) so I'll keep posted. The DVP works well. Sounds like you put a lot of work into this. Just out of curiosity, Do you ever use an air density gauge. That and exhaust temps were used a lot in karting. Anyway thanks and keep us posted.



This is only done on the brass needles (EMP,EMR...)- NOT the Yamaha anodized/plated aluminum needles (DTM,DVP,DVR,DRS,EKP,EKR...)


Adding a taper is a delicate process of polishing off the material and measuring the change against a known reference needle - say your original DVP that works so good from idle.

Starting with a brass needle - EMP ; It has a straight diameter of 2.735mm. Set your calipers to 2.725mm and hold it horizontal. Now set both the EMP and DVP needles in the gap until they bottom. Compare clip locations. The needle that rests lower has its taper start closer to the top and will run richer as it's taper point crests the nozzle first. Further down at 2.515mm the needles will be 4 clips different in height (middle codes- M,P,R,T,V). Changing clip position will offset the taper point higher or lower relative to the slide.


If the EMP#2 works best in the midrange and you want to put the DVP#4 taper on the EMP needle, polish and keep comparing the 2 needles at 2.68-2.73mm until their relative clip positions (EMP#2/DVP#4) line up in this range. This is near the first taper start and is a very narrow range of about 5mm. When it is almost identical, polish the modified needle with steel wool. This will leave it much smoother and take that last .005 off. When you're done the taper will start about 1-2 clip positions higher than original when the calipers are set to 2.725mm.

-The same process can be used for the third taper towards the needle tip. You can only increase the taper here. It is much less critical on the third taper because a wide range can be offset by the main jet. As you have seen going from the #178 down to a #165.

James Dean

Clark & James,

If you ever get your machined needles to work properly, you could start your own WR/YZF needle business!

I will be first in line to purchase a tested and proven new designed needle!!


I've been thinking about that alot. The profiles are the "proprietary" info that have taken all the time to develop. Does anyone have a good method to put tapers on needles with a precision lathe?

I have 2-stroke profiles down to a science too.


James Dean

Great minds must think alike as the way you describe modifying the needles is essentially exactly the same as what I have done in the past for a few four strokes.

As to the needles I receive them today and will start my mod process after a little more thinking. I did have my letters crossed up in the last post I now have a EMP, EMR and a EVQ in brass from Sudco. Actually for what I'm about to do the Q may be a better starting point.

You mentioned your EMP is now a tripple taper and I assume you blended the transition onto the origional taper at the start and cut a steeper taper for the last few mm of the needle?



Comparing the EKP#2 and DVP#4 (your preferred settings), and the needles relative position at 2.725, it appears they are about 2 clips apart. This may explain the hesitation, looks like more lean with the taper starting 1-2mm lower using the EKP#2. A richer pilot or the EKN#2(EMN#3) might fill in at this lean "spot" in the throttle. Ideally the EVQ#7 or EMP#3 with a short (5mm) extra taper will smooth it out.


Note: Here is "Bob M's" '99WR settings

YZ cam timing


air box lid cut off

PJ = 45

Air jet = 75

EMN needle #4 (EKN#3)

Fuel screw 2 1/4

Main jet = 168

Results: No loss anywhere from DTM#3, improved midrange noticed on fireroads and uphills, did not change ANYTHING but the needle. Only one full day riding to test at this point.


James Dean


After carefully measuring the needles I have already started modifying the EVQ and noted how close the EMP and DVP were at the start of the taper and concluded that a blended taper starting at 2.5mm above the taper on the EMP along with a slighly richer pilot or fuel screw setting would probably do the trick.

However, before I mess with my EMP I will try the EMP as delivered and a richer pilot setting.

On the EVQ I'm in the process of doing a tripple taper to bring in the main jet as you approach WOT. The taper I have put on this needle is really custom and I would have trouble repeating it.

Will be testing next weekend.

Thanks for the Info



Take note of how many clip positions richer or leaner it is than the EMP at 2.50mm, 2.45mm, 2.40mm, 2.35mmn and 2.30mm. For a given diameter, if the clip positions line up you will have taken off .064mm at that location.

(.016mm/clip X 4 clip slots (EM -> EV) = .064mm)

-If you follow the logic, the needle profiles can be graphed relative to the known reference. In this case the 1.0 degree taper decreases in size .0175mm/mm and each clip is .9mm. (.0175 X .9 = .016).

-All my modified needles are graphed to identify the throttle position and change in jetting. Sort of like putting in a variable main jet and having a number to look at for each throttle opening. The next best thing to fuel injection.


Look at september Dirt Rider. It appears Yamaha has corrected the stumble problem on the 2001 426s. They did this by changing carb setting to recalibrate the acelerator pump. Maybe our staff engineers should be looking at this along with the needle. I bet Clark and James will have this problem solved before they even get to look at a 2001 carb.


The stock fuel delivery stream from the accelaerator pump can be too long-- this is the basis behind the P-38 lightining its shortens the delivery stroke, amoung other things. Already adjusted the pump with the help of Factroy R&D guys, a P-38 tweaked, a lot of personal testing and have the jetting dialed with the DVP needle with no stumbles or problems.

I have used James Deans recommendations relative to the EMP needle and developed a custom profile for the transition from straight to taper based on the DVP needle and will test it this weekend. I'm very confident that it will be a outstanding performer but cannot claim success until I runs my standard 54 mile test loop more to follow.

James thanks for the insight and help


[This message has been edited by Clark Mason (edited 08-09-2000).]


-The '00WR may have a shorter stroke on the accelerator pump than the '98/99WR. I measured the rod travel and noticed it was not using nearly the available diaphram stroke. Still, I'm not convinced that the flow rate on the '01YZ/WR (or the P-38) will be increased, only the timing of how long it pumps. To increase the flow rate would take an increase in the nozzle hole by the slide or a substantially stiffer spring at the diaphram.

-Either way I have seen my '00 WR hesitate with no change to the accelerator pump, brought about by using a lean pilot/pilot screw setting and a lean needle.



Eager to find out which main gets the top end back... #165 - #162 ?? I tried to milk it out of the 426 owners before but nobody responded.


Originally posted by James Dean:

Eager to find out which main gets the top end back... #165 - #162 ?? I tried to milk it out of the 426 owners before but nobody responded.


Are you referring to the use of the E* series needles here?





DVP#4, 178MJ, 94MPH

EKP#2, 165MJ, 91MPH


If the #162 gives a top speed of 94MPH this will be 6 main jet sizes smaller to compensate for the change in taper. Keihin makes reference to switching 2 main jet sizes when switching to a significantly steeper taper needle (triple taper). This is on the PJ/PWK 2-stroke carbs that have more taper to start with. Since EKP is a single taper needle, will a new "triple taper" needle need a #160? #158? We are all very lucky to have Clark around doing a controlled test and allowing us to hear his results.


Originally posted by James Dean:


DVP#4, 178MJ, 94MPH

EKP#2, 165MJ, 91MPH

I was asking, because that's what I found when I made some test runs with a EVP needle last week. I had ordered the EVP last year, because I figured the steeper taper could help with the lean condition in the upper range. But I didn't use 'radical' settings (clip position, main) back then, and so the EVP behaved like expected: too lean on the bottom, too rich on top. Last week, before my ordered EM* series needles arrived I decided to give it another try based on the recommendations on the EKP needle.

First try was EVP 7th clip, 165 main => strong bottom, excellent midrange but a little flat on top. Went to 175 main, strong top end back but plug started to fould after a few test runs! Back to a 170 main, lost on top, but no plug fouling.

Just out of curiosity I went to clip pos 6, but then it felt lean on bottom and mid. Never tried clip 6 and 175 main.

It seems clear, that the bike needs a main >= 175 in the opened up version to run at its full potential, regardless of the needle. Also it seems clear, that while providing a great mid the E* series needles are too rich on top. Maybe reducing the fuel amount from the pump can help, but I think either a triple taper (DVP on bottom and top, EKP in the mid) or a taper angle between D and E would be the solution - neither is an easy task!

Just though of something else: the main air jet. Yoho, one more variable :)


[This message has been edited by Drehwurm (edited 08-10-2000).]


Is the needle you are using truly a "EVP" is this what is stamped on the needle. A EVP although a 1deg taper the taper starts much further down than the EM* and as a result the diameter of the tapered section is always wider than the EM* needles and a larger MJ will be required. There is a very tricky balance here. When I recorded 91 vs 94 mph these are vary similar readings and I felt both jet settings were working pretty good on top. Remember I'm doing this on the street on a approx 1 mile section with a slight uphill grade using 14/47 gearing in a fairly tricked our WZ 420. The 94 vs 91 probably has more to do with when I started, when I shut down or how much tucked in I was on the run, but as stated before the bike felt responsive on top.

This weeked I will be testing a modified EMP needle and we shall see.


Michael and Clark,

When the EVP is in clip #7 it equals an EMP#3 and EKP#2. The nozzle restriction at it's narrowest point is the same relative to the slide in these clip positions. Therefore the fuel flow is the same within any measureable quantity.


The #165 was "flat on top" and the #170 "lost on top compared to the #175", can you describe what you mean here? Did the #175 main accelerate better to a point where the #170/#165 would maybe rev out better? :)

What is your bike setup and altitude/temp?



[This message has been edited by James Dean (edited 08-10-2000).]

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