Jetting EKP vs DVP


What do Sonny & cher have to do with this :).


99 WZ, all YZ mods, de-octopused, OEM YZ tank and IMS seat, jetting by Clark/James, got forked by Pro Action, DSP airbox, PB Header, Stroker SX-1 SA, Thumper Rad Guards, Acerbis Hand Guards. Moab, HERE I COME!!

I've been following the on going R&D process undertaken by Clarke and James with great interest.

I have a 2000 WR, YZ timed, stock everything. I recently modified the stock muffler (Oz version - cut off welded end cap and removed the 3/4" outlet, replaced with 1 3/4" - more explanation available if anyone's interested).

It seems to have picked up gobs of bottom end :D - it will pull hard from 60km in fifth, which it didn't do previously - but the mid-range still seems a little sluggish. I suspect it's running a tad rich (the inside of the muffler had a bit of carbon deposit when I cut it open).

But anyway, to get to the point... It seeems that Messrs Mason and Dean have settled on EMP/EMN as about the best performing needles, with mains still undecided. Is this so?

Also, using the example of EKP and EMP, do they have different characteristics or is it just the clip position used to get the particular height?

Final question - my local dealers (in Melbourne) don't have EMP or EMN on their parts fiche for WR or YZ and don't know anything about them. Are they Yamaha parts or generic? What are the part numbers? If not Yamaha parts, where do I get them?

Sorry to be so wordy. I'm rapidly coming to grips with the concepts youv'e been discussing - just a few more bits of information and I'll be there (wherever there may be :) )

thanks in advance



The needles I'm currently working with are the EMP and EMN. I started with the EMP modified it around the transition zone from straight to tapered section and a little more taper toward WOT. This modified needle works excellent and adds even more punch to my WZ 420. I do not think I can duplicate the exact profile I have on this needle without a hell of alot of detailed work.

However, after graphing the exact profiles of a range of needles (thanks James Dean) I feel that a modified EMN needle at the transition point from straigh to tapered section will come close and should work fine.

I have on order 4 EMN needles and I plan to modify one of them and if my predictions hold true after testing I will duplicate the mod to the other three. It will be awhile before I get to this project probably three weeks or so. Running with the EMN will require the normal fiddeling with the fuel screw but the mains will be the same probably between 160 to 168 but testing will refine it.

The EKP and EMP are identical except the EKP starts its taper one clip position sooner than the EMP. I worked with the EMP so I could dial it to the #3 or #4 clip position for my normal altitude riding (1200 to 4000 feet) and still have at least two clip positions each way from my typical riding conditions.

Needles are available from:



To All

OK I got my custom tapered EMP needle back from James Dean and ran my standard course with it to rebasline my thinking. I then modified a EMN needle, based on my previous testing and interpreting James Deans charts, to richen the trnasition from strait to taper. I blended then EMN slighly from 2mm above the taper start to about 3.5 mm below.

I hit a home run on this one!! This needle preformed great it exceeded my expectations and was better than my EMP modified needle and easier to do I think I can make this one.

This was todays set up.


PJ= 48

Fuel Screw = 1.5 turns out

needle EMN modified #3 from the top

This combo worked excellet smooth on the bottom no to extremily lite poping on decelleration and when you whack it wide open its hit city and wheelie time. I love poping those 30 to 50 MPH third gear wheelies!! I must admit that a little tinkering will garner more performance for you riding conditions but I knew that but I was lazy thinking James Dean would solve the equation for me but thats not possible since James Dean does not ride where I do. So we collaborated and it worked out great. James had the detailed graphs and when I saw where my modified EMP needle fell relative to a EMN I knew exactly what to do, Thanks James.

I took a altimiter with me on my standard test loop it varies from 800 to 3800 feet in altitude!

So based on this success since I'm going to Troy meadosw next week I modified a EMR needle for higher altitude work. I let the forum know in about 10 days how this worked out.



Great to hear of your success!!

The EMR will be an interesting test of a much leaner modified needle. Will you start higher and take more off using the same clip position or ...?

And, do you think the FCR and FCR2 carb changes are a factor here?

James Dean


(Kevin, were you interested in a modified needle yet, or do you want to wait?)

I've lost my jetting cherry! (thanks to Clark and James... inspirational :)


I have a 2000 WR (Australian) It seems to have a CR carb (doesn’t say “CR2” on top just CR). YZ timed. Stock (same as Canadian?) header with final baffle in muffler opened up from 1" to 1¾". Air box lid removed. Riding at about 2000 feet (600m)

Original/stock settings:

Main 165

Needle DRQ#4

Pilot 40

Screw 2


Idle: Starts easily w/o hot start unless ‘hot’

1/8: plods, doesn’t stall, slow revving.

1/4: sluggish/slow to build revs

1/2: comes alive and revs cleanly through to full

Full: fine, no real increase in power over ½ throttle though.

Generally: pulls well down low, but has a definite increase in power at about ½ throttle. Pops a bit when backing off on downhill.

New Settings:

Main 160

Needle EMP#4

Pilot 40

Screw 1½


Idle: Harder to start. Needs Hotstart open to start, even when not hot. Stalls if throttle snapped from idle.

1/8: possibly stalls easier than before

1/4: much more responsive to throttle

1/2: similar pull to before but more snappy!

Full: seems ok still, but I haven't wrung it out.

Generally: Much punchier. Power comes on earlier and harder. Misfires on constant throttle at about ½ to ¾ (100-120 km in fifth). Seems to get hot quicker after starting. More popping when backed off.

Overall, a rewarding experience. Having read Clark's latest post I was inspired to order an EMN and will try his set up next. I've noticed that everyone else seems to run a bigger pilot than mine? It came stock with a 40 and a spare 38. Is there something different about the carbs in the Oz bike?

What does all this mean? ie. rich/lean in midrange, what's the missing about? What does the popping mean? If it's rich low/idle and lean at mid, does that mean go for smaller staight (EMN) or move the clip or change the pilot or screw? Incidently, at one stage it was missing on about 4-5k rpm(steady)up a hill in third or fourth and I pulled the choke on a touch, then it picked up (I couldn't repeat this - maybe fluke). I tried pulling on the choke a touch on the freeway while accelerating from 105km in fifth and it seemed to be a tad worse than without. Doing the same with the hotstart button had little or no effect.

Any insights greatly appreciated. Ithought I was coming to grips with the jetting talk, but obviously I'm a ways off yet :D

[This message has been edited by Andrew Perry (edited 08-28-2000).]


The EMP has a smaller straight diameter by a very small amount =.01mm(richer at 1/8). Not sure why you need the hot start for starting all the time though. Does it need to be idled up a little? The pilot screw may then be backed out to the original position or out further to compensate for the needle taper starting lower on the EMP#4 (it is leaner at about 1/4 than DRQ#4). This is where Clark has modified and added a short transition taper. EMN#3 or #4 may be the answer.

Lastly, the main may need to be reduced more if this is over-rich at 3/4.

-Was anything else changed?



I do not think the FCR to FCR2 is a major player in the jetting equation we have been working on. With the EMR needle I will run it in the #2 clip position (Since the transition starts earlier than on the EMN) and modify the taper transition just like my EMN mod, run the same 48 pilot but the fuel screw at 3/4 and a smaller 160 MJ. This will be my starting jetting for (7000 to 10000 ft altitude). By Wednesday night I will either have it sorted out or I will go back to my previouse DVR high altitude jetting and enjoy the riding for the next 4 days. I have high confidence that the EMR will work well.

I will post my results next week.



Sounds like a good plan on the needle clip and mods. This needle's straight diameter is .03mm bigger and will be a big step. Much more than an EMN vs EMP, hope it works. Maybe will want to compare it's taper start relative to clip position to your previous high altitude needle setting with the DVR.

The FCR question seems like a small factor to me too, but is always lingering when the others post questions having used the DRS and DRQ in the '00WR models. Still waiting for a 426 owner to try an EKP or EKN...

James Dean


Thanks for your help. I should have mentioned that I removed the airbox lid between jetting changes.

[This message has been edited by Andrew Perry (edited 08-29-2000).]

...and, Is there anything in my changes that would cause it to run way rich on idle (hence hotstart button)? eg. smaller diameter on needle. Why the increased popping? - fuel screw? Is the misfiring on steady 1/2 to 3/4 due to rich or lean?

I'll try your recommendation on the EMN #3 and let you know how it goes.

Your posts (and Clark's) have been a great help. If it's not too much to ask, could you post an idiots guide to reading the jetting symptoms :)

[This message has been edited by Andrew Perry (edited 08-29-2000).]

James & Clark,

It's been great following your progress on the jetting front as this is a subject I would've never normally attempted, but you both inspired me to experiment.

My '98 WR came so bably jetted it caused all sorts of problems - starting, popping, fouling plugs etc. On Clarks & BajaDesigns guidence i went to YZ timing, a DVP#4, 175-80main, 48 pilot, fuel screw 2turns & de Oct-d (100airjet)

Airbox lid removed, various exhausts. the bike ran great, always started 1st/2nd kick. Then james threw in a varient - more mid range boost PERFECT!!! I ride dualsport, Enduros and any other offroad I can. I tried the EKP#3, 165main, I left the pilot and fuel screw alone. The bike really rips no stutter or hiccup when the throttle is wacked open, I tried what Clark did, 30mph in 3rd (15/50 gearing) cracked open the throttle and the bike lofted the front (albeit only slightly i wasn't trying to wheelie and was sitting very forward)

I just love it...Thanx guys.

You've both made an Englishman very happy.

I am curious - has anyone else had good luck using an unmodified EKP or EMP needle?


Glad to hear it's working good for you.

I have one other riding friend with the EKQ#3 unmodified (1 step leaner) working good in his '99YZ400.



Yes I am ready for a needle any time you think the R&D is complete. I am riding my 99 at sea level + 1000 feet. I am still waiting for my DSP airbox and PB w/ Stroker SX-1 silencer.

Let me know James when you are ready!

BTW, Florida, as usual, was wicked humid during my family's vacation. It is nice to be back to NH.



99 WZ, all YZ mods, de-octopused, OEM YZ tank and IMS seat, jetting by Clark/James, got forked by Pro Action, DSP airbox, PB Header, Stroker SX-1 SA, Thumper Rad Guards, Acerbis Hand Guards. Moab, HERE I COME!!

Just got back from 5 days of riding up at Troy Meadows. My altitude varied from 6000 to 10000 feet with most of the riding at 8000 feet. The EMR needle did not work out even with several mod attempts. It was cool with temps from 50-75 during the day.

So I ended up running my modified EMN needle in the #2 clip, a 45 PJ, fuel screw at 3.0 and a 165 MJ. Bike ran conistent but not inspiring like it does a lower altitudes. Don't know if its crummy jetting or altitude, I think its the altitude. I never did put in my standard high altitude jetting of DVR #4, 48PJ, 3/4 fuel screw, and a 175MJ. Probably should have but felt like riding vs tinkering.

The riding was oustanding as it had rained for two days before we got up there then rained again making conditions perfect on Friday and Saturday lots of traction, no dust--never changed a air cleaner!! and no front wheel washout it was great. Only had one get off I center puched a tree a big tree but no damage of note to bike or body.


Clark, Sounds like you had a GREAT time. I'm sorry I didn't make it up there,I ended up going to Gorman MX on Sat. I met up with Cliff from the YZ board,(he's a GOOD rider).

I stayed the night at cottonwood campground and sunday morning SLO"fast" JT and Harold from the WR board met up with me and a few of my other buddies and we rode the forest trails.

We had a great time, a couple of spills, ( one concussion) But we all survived.

We'll have to meet up with you next time though. By the way, were all the regular trails open? How severe was the fire damage to the riding areas?



So Cal Erik

Visit my club's site at <A HREF="

" TARGET=_blank>


So Cal Erik

All trails except the Moghany connector from Troy to the top of Rattelsnake were open. The main fire damage was south and east of the main trail network. The fire totally trashed the DomeLand wilderness. It started many miles south and east and worked its way up onto the Kern plateau. Fire came within 400 yards of Grumpy Bears and all the perminate residends of Kennedy Meadows are very thankfull and appreciative of Fire Figthters.

I rode the Cannel trail all the way down to Big Meadow and saw no fire damage. When we got down to Big Meadow that end of the trail said it was closed--don't have a clue why??

All the stuff on top Beach Ridge, Jackass, Jackass peak, Albineta, Granite Broder, Blackrock Mountain, Little Horse, Beach, Monache, Rattlesnake, Bonita Connector, Fish Creek, Schaffer meadow, Stony Meadow, North Meadow, the Sherman Pass Jeep roads, etc. were all open. To get to Bonita meadow is a long ride but can be done on trails.


Right on!!!!! Let me know when your next trip up there is, I'd love to go, if I can get a hall pass from the wife.


So Cal Erik

Visit my club's site at <A HREF="

" TARGET=_blank>


Thanks for the update Clark. :)

Lately I've been trying a few more modified needle combinations on a quieter exhaust setup. Haven't gotten it to my satisfaction yet. Will follow up with more later.


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