at last, snap off the bottom & 3/4 throttle response

nice one jd

you'll note from my previous post how i mention that a DPM needle would be nice.

sounds like we have both found different ways of sorting 1/4 throttle. i've gone large jets & you've gone with the APJ still.

where on the needle did you decide to start each taper?

with my needle on EKP No 7 i should have had a good ride instead the bike was rich. you have an even thinner needle at 1/2 throttle+ & yet it's going well?

i've been e mailed overnight by 2-Dads & my powerbomb/stroker 'zorst is ready. traditionally an open pipe is worth 8/10 on the MJ. if i'm lucky my misfire on the 'E' needle may clear itself up a bit.

maybe i've pushed the bike as far as it will go on the standard exhaust.

i've certainly pushed the gearbox!

i hadn't heard of the difference in breathing to the airboxes. i'll look for this next time i see a '00 YZ or WR.

i see we both rate the M or in your case M or N as the best straight.

when you get the PAJ-Screw you'll have to try a different route in.

i think that lifting the needle just one clip in test one & disconnecting the APJ was a little unfair on the bike!

how are you machining your needles jd? i've more testing to do but i need a 'E' start & 'D' from halfway AS IT STANDS. i get the feeling a proper exhaust is going to help.



As you said you may be just refining the settings for you current conditons and it may not hold up when applied to a braoder population of enviromentals. I felt just like you last year when working with the F** triple taper you sent me along with the AP adjustments I was trying but it did not hold up across all my riding conditions. I think both you and Taffy are on to something and with the easily variable AP setup I'm sure you will evolve a better solution. Hopefully it can be easily, or faily easily repeated so some others can benefit. My feeling is still there is magic to be had between the AP pump stroke and the correct needle transistions as this bike has always had problems with this with transitions and still being able to handle steady state as in part throttle crusing.

Keep up the excellent work and keep posting as you reach valued conclusions.

Thanks for your efforts


I wonder what Doug Dubach thinks about all this.

James, Taffy, and Hick,

Just wanted to add my thanks (which unfortunately is all I can contribute of value) to you all for posting the results of all your testing! I keep "lurking" around this post - reading and learning. There is a ton on information to chew on - Thanks again!

i know exactly what doug dubach thinks

he respects the work that we do

he knows that we swim in the dark & that he knows where we are EXACTLY

he enjoys watching us unravel things that he did in 1999

he won't give us tips unless we've earnt them

he wouldn't see us struggle forever but he won't stop us struggling

we've got to earn our info

if you ask "what makes 'em go doug" he'll reply "petrol"

if you say "doug i've got a delay at 1/4 throttle" he'll say try X.

if you say i used to use X but found that Y was better he'll say you might find Z will be "very good". but what he won't do is tell you that Z makes the bike go when the question was "what makes 'em go doug"!

you earn your smarties (hick that means candy).


I went out pulled of the carby scribed my pump rod and accurately measured my accelerator pump stroke and it was 0.052" or about 1.31mm this is a little shorter than I reported earlier in case any of you AP experimentiong types are interested. Stock it was 0.120" approx 3mm. So mine is shortened by over half.


i have just read the old (& very long) post from last august about the EKP v DVP.

i can see now how you 'machine' the needles; but it's not my cup of tea.

one or two things come up such as the need for an open exhaust with the 'E' series.

so many of clarkes tests scream out for the 125 PAJ, it's staring at me it's that obvious.

the exhaust should be here by the weekend.

has your american history taught you the story of amundson & scotts race for the pole.

it's getting to feel like that JD!

i found your result reports slightly vague so i might quiz you some on your findings.

i feel that by sticking to standard needles my quest may help others if it also comes to fruition.

what i don't get is how my bike ran well with EKP No 7 & yet runs so badly later in the week. was my gearbox going last sunday during test 6 +?

then i have this ridiculous situation of was it a misfire in the freezing dark or was it fifth gear! quite stupid.

it could turn out i had it right all in one day & all i needed to do was do a seventh run WOT & plug chop. then run it with a 162 MJ.

we'll see.

i'm about to tackle the jetting from three ways. the first, with a 'D' needle.

i have ordered a DMM needle today. the idea is a middle clip, narrower version of the DVP on clip No8. i want to give the engine as much help at tickover & 3/4 throttle as possible.

secondly, the EFP. i've been told where i can get drills that go in increments of 0.1mm. apparently the MAJ is simple to work out; 200 =2.0mm hole!

so i'll order 2 or 3 drill bits tomorrow. the idea is that if the PB/stroker doesn't help-a 210/220/230 MAJ may (leaning off the top end).

thirdly, i hope to be able to afford an 'emulsion tube' & drill this out from 2.9mm to 2.95mm. this does seem unlikely however. within this i would put an EKT needle. really early taper start, my 1/4 throttle system & see what happens after that.

i've spent this evening checking how far into the ET a needle sits. i measured my EFP needle & the straight sits 6mm down into the tight throat of the ET. the tight part measures 11mm long.

although a restriction is a restriction; if it is a very short restriction as opposed to a long drawn out one more fuel must flow at tickover.


[This message has been edited by Taffy (edited 02-27-2001).]


The position of the carb needle taper start could easily be misinterpreted. It would be better to indentify the length of taper regardless of which straight diameter is used. Then adjust the clip position to match the state of tune the bike is in. For example, take your OCEFP needle to a machinist and have him grind a .5 degree taper for 3-4mm at the start of the original 1 degree taper. This is the best improvement you could make to a standard brass needle.

I have a machinist do the needle grinding when a profile is established that works well. During testing and experimenting I will put a brass needle in a drill press and use wet/dry 400 grit paper followed by 600 and then steel wool to grind a custom profile to test. It provides instant feedback to modify and then ride and compare. Immediately after, write down notes on the change, measure, and graph it. This simple approach allows a mapping of where the improved jetting can be found.

Last summer when I first got the WR, this sequence was run through and that's when the posting was made to TTalk members about the EKP needle. Then a few months later Doug Dubach and Company came out with the needle in both the YZ426 and YZ250F. It would be interesting to know how they arrived at their settings. Wonder if Yamaha noticed the sudden surge of orders for the EKP needles. :)

If you really want to understand the role of needle tapers, their positions, and get the most out of your bike you must ride and experiment with different straight diameters, tapers and clip positions. The graphs are a map and compass (North Pole is richer). There are no anomalies to jetting with this method. Results are predictable or at least can be explained.

In 1998 I looked at a YZ400F shop manual and thought the DVP needle was an odd choice, too little taper and too lean on the straight diameter. Then after riding one, the impression matched the prediction. Turned the throttle from idle and it bogged & died, mid-throttle didn't have enough response to change at the grip. This may be good for control and smooth power, but many riders want a more aggresive response. The '01YZ's have the right approach and will work for most. High altitude (Colorado) bikes will be fouling more plugs though, unless they go leaner on the clip or switch to EJQ/EJR.

Study the graph, and chart your course before you go explore-

Keihin FCR (Thumpers)-

Keihin PJ/PWK (2-Strokes)-


[This message has been edited by James Dean (edited 02-27-2001).]

About drilling the emulsion tube:

(Been there, done that)

EKT#4 in a 2.95mm ET is the same result as EFM#5 in a stock 2.90mm ET

2.95-2.77 = .18 = 2.90-2.72

You will never know the difference in CSA because the tapers both will start at the same point.

You're fighting windmills Don Quiote. :)

Taffy - Yes! At least the older products of America's public school system know the Amundson & Scotts story. I'm concerned about the current generation however - too much PC Crap! Your example (A & S) is a great one - I keep getting the sense that it is more like Ali - Foreman sometimes!

Thanks again for the lessons you guys!

no you are wrong old friend.

you're maths equations are wrong not your ability to do them.

the CROSS SECTIONAL AREA of the standard EMULSION TUBE at 2.9mm diameter is;

pye x d (2.9mm)= 9.1118mm2

any 'M' needle

pye x d (2.715mm) = 8.5305mm2

take A -B = 0.5813mm2

0.5813mm2 is the right gap for a nice tickover. OK?

drilled tube figures

2.95mm x pye = 9.2689mm2

now we want a needle straight taper that is big enough to leave us with the 0.5813mm2 gap.

9.2689mm2 - 0.5813mm2 = 8.6876mm2

so now we need a needle that is 8.6876mm2 in CSA.

_ _ R needle = 8.6562mm2

_ _ S needle = 8.6876mm2

_ _ T needle = 8.71905mm2

so the _ _S needle in a drilled tube will have the same tickover as the _ _ M needle in the standard tube. this figure is correct to the nearest 10,000th of one millimetre.

you're only one letter out JD but more importantly your way of getting there was neolithic.

so why did i say a _ _ T needle when my calculations say _ _ S? well due to the extreme height of the start of taper of an _ _ S needle in the ET, i decided that more fuel would find it's way past the side. therefore i "added a letter" to "bung the hole a little".

one of the biggest floors in your jetting is that when you said that;

"Now study the graph I posted before on needle profiles. We don't need a larger emulsion tube (ET) because a smaller straight diameter AND a richer clip position create the same result".

i'm trying to get the taper to start when I say & keep the same setting needle taper. your simplistic answer was to lift the needle & richen the 1/4, 1/2 & 3/4 throttle setting as well.


EKP moved from clip 4 to clip 7 in my tests = a 2.7mm lift in the start of taper.

going from _ _ P to _ _ T straight is an increase of .04mm in dia & using your rule of .0175mm larger straight = 1mm higher taper, that means that with .04mm larger straight the taper start has gone up 2.3mm.

that's still .4mm too lower start of taper. but to put the _ _ U in would have leaned tickover even more (i've gone from S to T already).

& we can't drill out from 2.95mm to 2.96mm coz they don't make a drill bit that size!!!!

what did don quiXote ride jd?


Since we are disecting the details of my charts and methods, there is more. The question of being a purist or practitioner.


In the chart, the sloping lines are shown straight. They actually should not be "perfectly" straight. The area for fuel to flow is:

CSA = 6.605 - (Pi/4)x(2.715 - .0175 x L)**2 (mm2)

where L is the throttle position beyond point where the taper crests the ET.

Using simple calculus, taking the derivative determines the slope:

dCSA/dL= (Pi/4)x(.0950 - .0006124 x L)

and rate of change of slope, second derivative:

d2CSA/dL2= -Pi/4 x .0006124 = .000481mm2/mm2

The slope at the start of the taper (L=0) is .0746mm2/mm and the slope 20mm further open on the throttle is .0650mm2/mm. This is a decrease in slope of 14.8%. Furthermore, the fluid flow rate is really what we need to compare and it is not linear either. In this case, the increase in fluid flow is opposite the non-linear effects of the CSA. The change in slope with all things considered is not worth including. It is a matter of functional application.

Simply stated, the graph works for practical purposes.

Didn't need a textbook for that Taffy, how is my math now? :)


BTW, Did you hear we had a EARTHQUAKE 6.8 magnitude? Stuff was falling all over and we have not gone back to work yet! Maybe I'll get to go ride on Friday.

[This message has been edited by James Dean (edited 03-01-2001).]

touche, monseiur!


Oh my gawd:P I never thought I'd see calculus on TT. Brings back bad memories of college.... EEEEKKKKKK!!!!!!

Next thing you know JD will be throwing out Laplace transforms and fourier series :)



have you tried an "F" series needle F_M could be the go, also I am in doubt as to the removal of the AP, I believe that in a single cylinder engine at low horsepower the AP is needed for quick throttle response compared to a multi-cylinder with more horsepower in the low - mid rpm range and slower throttle the AP is not as effective.JUST my opinion (could be wrong?)




YZ timing,EKN needle, VORTEX dualcurve ignition

SF triple platinum s/plug

open box -unifilter

98oct fuel

Staintune s/s open exhaust& header......

Somebody stop me !!!


[This message has been edited by NH Kevin (edited 03-01-2001).]

And I thought I was fun at parties! I want to party with you Dudes! :)

Now we can all discuss windage losses on impulse (stage) turbines and why a Curtis Wheel turbine is best used for the astern engines on a submarine/target...oops, I meant surface ship!

And then we can jump right into Alpha, Beta, Gamma, Neutron, X-ray, Cosmic and all the different forms of radiation that make this world just such a fun, yummy place to live in.

[This message has been edited by NH Kevin (edited 03-01-2001).]


you're looking at what you're giving away...

look at what you're putting in...

50PJ &...

140 PAJ this is the slow speed enrichening circuit, i introduce tons more air which is going to suck up a very very rich mixture...

it's designed to work at 1/4 throttle & about's.

already JD & clarke are reducing their DURATION of squirt to almost 1/4 throttle. i mean, forchrisakes! .8mm pump lift etc etc!!! you know!

but all the time they can't control the amount in that .8mm because there is only one outlet size made.

to be honest with you andy i don't give a **** , you know. i'm gonna put one more superpost up in the next fortnight & if people haven't tried it & spent their eleven measly dollars & tried it they can all take a flying **** !

i don't recall calling JD a liar when the needle (EKP)didn't work first time out. i wouldn't rubbish anyone's work unless i was convinced about what i was saying.

sometimes andy a man's gotta do what a man's gotta do & i don't mean shoot the **** !!!

my arse is hangin out in the wind & all i hear is everyone else going "i spent $460 aus dollars today on an ignition, do you think i ought to spend $11 usa on a PAJ-SCREW".

do you get my drift andy. good. i haven't forgotten your first post. what i'm saying is as an englishman i have a more positive attitude than you.


[This message has been edited by Taffy (edited 03-01-2001).]


I could almost guarantee there is not a soul on this forum that doesn't value all the R & D you have put into these horrid carbs. I am anxiously waiting your final answer. In fact, I am very eager to start ripping apart my carb. But alas poor Yorric, I have a kid-friends TTR 225 I promised to fix. It has been OOC since June, 2K. He purchased it in March. I must put his bike before my own.

how do you measure the stroke on the accelarater pump?

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