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

Hey guys, the pump actuating ramp on the back of the throttle shaft can be machined or filed down to give slower delivery rates! No need to change the outlet size :)

Taffy,I dont mean to sound like I'm disagreeing with you on the AP but this Aussie dingo brain of mine can not under stand how it would be better without it.I understand what you are doing but it seems like there might be a problemin in getting the jetting right for both constant throttle and quick blips of the throttle e.g.jetting for constant throttle would be lean when throttle is opened quickly and jetting for fast throttle action would become rich for constant throttle, thus the reason for the AP.Or maybe I should just shut up and go chase some kangaroos or something! Actualy that's not a bad idea. :D:D

P.S could you start a new topic called At last, snap 2,as you know you cant ride computers so mine is a slow prehistoric dinosaur and its taking me almost 10mins to get down here :D




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 Andrew in OZ (edited 03-01-2001).]

[This message has been edited by Andrew in OZ (edited 03-01-2001).]

Ali - this is turning into a WWF Royal - Rumble. Can't tell if this is an engineering lecture or a streetfight. It fun in any event!


Your enthusiasm is charming. I wish we could be discussing this over brews at your local pub. :)

Unfortunately your math is wrong. I was trying to keep it as simple as possible (neolithic if you will) to avoid a page of calculations that can get boring. I said "you will never know the difference".

Your obvious mistake is that the CROSS SECTIONAL AREA is not:

Pi x d , THIS IS THE CIRCUMFERENCE in mm, not mm2

The CROSS SECTIONAL AREA of the standard EMULSION TUBE (d=2.9mm) is:

A1 = Pi x d x d /4 = 6.605mm2

for a 2.715mm 'M' needle

A2 = Pi x d x d /4 = 5.789mm2

A1 - A2 = .816mm2

So now you want this area with your 2.95mm modified ET.

A3 = Pi x d x d /4 = 6.835mm2

and to find the desired needle,

6.835mm2 - .816mm2 = 6.019mm2

Lookin for the needle with this area,

--S needle = 6.005mm2

--T needle = 6.048mm2

The answer lies between the 2 needles and is NOT going to be EXACTLY the same!

Many years ago I did calculations this way and nothing has changed. Stick with the simpler method when dealing with this. We are dealing with a DIFFERENCE in area which is proportionally close to the gap within a small margin.

The forum readers will more easily remember to compare the EK- needle diameter to the hole diameter (2.90 - 2.72 = .18mm) than the area of a circle is 3.14159 x d x d /4 and all the other calculations above.

Yes, Don QuiXote thats Pi with an I :D


You keep talking about how the needle clip richens mixture at 1/2 and 3/4 throttle while dismissing the fact that an increased ET will do the same. You must not ignore that an increased ET will have an affect on fuel mixture at 1/2 and 3/4 throttle to the same extent as moving the needle clip.

At mid-throttle (2.515mm diam) where an EKT#4/2.95mm ET has

6.835 - 4.968 = 1.867mm2 area for fuel to flow;

EKM#7/2.90mm ET has (2.515mm - 3x.9x.0175 = 2.468mm diam)

6.605 - 4.784 = 1.821mm2

The EKT#4 will actually be 2.5% RICHER at 1/2 to 3/4 throttle than EKM#7 due to the emulsion tube by a small margin.

If you want to raise the taper start and NOT richen the fuel mixture at 1/2-3/4 you will need to use less taper (D-- needle) -OR- a multi-taper needle -OR- change slide cutaway. Take the EKR#4 and reduce the cutaway to make it act like a higher taper start on a EKP#4. This was your idea many months ago, and it still applies now. Less accelerator pump and reduced cutaway together. My suggestion on 2/27 was to raise the taper start 2mm with a simple modification, adding a short taper. You could easily do this to raise the taper 2-3mm.

Be advised that there are limits to how much can be done with slide cutaway. The 80's Yamaha YZ's chased this using less cutaway and never got it right IMHO.


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

how did it go ?



i'm just pissed off, sorry lads. if you read from the top to the bottom i have arrived with this incredible power increase & breakthrough in our carb knowledge.

at the beginning lot's of curtious well done's blah blah blah.

then we have the doubters syaing like an eight year old boy "do i really have to go out in the cold to get to school"

"yes son"

"er! i'll just tidy the bedroom dad"

"no son go to school"

"aah! i've remembered i've got to go &...."

""son, **** off to school, there's a good boy!"

the classic is "i'm broke at the moment"

$10 & 1-hour!

you reach a point where all you're talking to are fence sitters & hand wringers. i have passed absolutely masses of info on & a month later it's credited to someone else or i get the "i always thought that the APJ delivered too much too soon & too late blah blah"

JD is the only one looking in his crystal ball.

boys you gotta get those old DTM needles out or even the DVP's put them up to clips 6/7 & put the PAJ-SCREW in!

one bloke when told of this suddenly had a bike that ripped off the bottom, did snap wheelies in 6th gear, pulled chicks, danced, sang & said "will your needle be better?"

as our ministers of parlaiment say "it's time to put up or shut up!"

the 'E' needle is going to be for racing when it arrives i would think simply because you'll have to be skilled to set it up for your bike, whereas the 'D' needle is just a bloody nice needle as clark has indicated that will do snap wheelies no problem.

when ian came over last friday to confirm my gearbox problem he couldn't believe the bike would do a snap wheelie in second gear on 15/50 gearing. (DVP, clip 8, 50PJ, 21/4 turns on PAJ-SCREW, 1 1/2 turns on PS, 170 MJ)

can i take this opportunity to apologise for not joining in with a lot of the "fun" correspondence as this thread has unravelled. i think the yanks would call me a bit 'tightly wrapped!'



As I was scanning through the 99 YZ microfiche, I see there are 3 (4?) different diaphragms for the accelerator pump. Taffy/James/Clark/Hick any idea on the difference? They do have differing part #'s...


I,ve been reading this thread for three weeks now, and I love it. Being a carpenter, half the time I don't have a clue what you guys are talking about, but I'm dying for the "recipe" your compiling for a kick-ass bike. I'd pay you $50.00 Canadian (thats not much in yank money) for a simple approach on how to make my bikes setup like yours. Some of us still believe Taffy, you can do it!

hi kev

the lads (JD) wanted these diaphrams months ago but they never came through. they have a taller & taller metal post in the middle to limit the stroke. although the 98/99 models could do with them, the 00/01 models don't.

they have a different APJ set up on the 00/01 models (apparently) that allows you to limit the pumps stroke. this has only just been spotted (hick via BK) & if you look above on this thread they have started to limit the pumps stroke & wean the bike off as much APJ juice as they can.

it's going to be very very hard work weakening one & altering all the needles & jets to compensate.



Taffy. In the process of trying your PAS. I am going on vacation in a week (spring break) and still have my #75 jet lying around, having put in my 100 when I "deoctopussed". I won't get the parts in time to try them out for my vacation (going to California and Oregon to ride) but I want to try your craziness out this weekend and see if it works when I have the time to do it... (Full week of studying ahead, and then we take off Sat at 8 AM) With all this math you guys have floating around, can you predict how big an orifice a 140 PAJ would be if I were to drill out my #75? I could pick up a bit, and have it done within your allotted hour (unless I screw up my timing somehow, not unlikely when you are me :) thanks for the help, runs like a champ). Sounds like an easy task, and I am willing to give it a whirl. Thanks for all your help.


strictly speaking you need a 1.4 drill bit. or a 1/18" for 1.41mm.

but i'm pretty sure that if you stick a 1.5mm drill through it & make it a No 150 you'll be OK. grind the No m75 off afterwards for your own reference!

try it with the 48 PJ. when you run it (w/o the APJ don't forget!) try your Pilot Screw (the one you can adjust externally) out 1 1/2 to 2 turns. if it pops on deceleration give it 1/4 to 1/2 turn more.

better to run it a little lean & feel the vibration at a steady 1/4 throttle & THEN open up the PS a little at a time to get rid of it.

remember buttonfly that you're young & enthusiastic! try to have a good ride as is for a little while. keep the PAJ No 150 in your pocket a little while. enjoy for a day, glitches & all as is (if you have any).


Thanks Taffy. Also trying to show support for your efforts. I figure if I can make it a little easier to try this for the fence sitters (I would imagine a lot of these people have the #75 around, and won't mind killing it) more people might. I am also trigger happy and wanting to do SOMETHING on my bike... ANYTHING. I ordered a bunch of parts (I warrantied my graphics through factory effex and their customer service was terrible) and I was hoping they would get here this weekend, no love. Too much snow around here to want to die... last time I went riding in the snow I was racing in a scramble, and cracked my helmet on a boulder... not real interested in doing it again... anyway, thanks for your effort, and I will try it out someday...


No accel pump

Cool temp 40F

#48 pilot


1 1/2 turns

EKN#6 modified with 2mm higher taper start ~.5 degree

#172 main

MAJ removed

The bike pulls hard and has good response off the bottom just as you said. This is very close to running WITH the accelerator pump jet(APJ) and having a leaner clip position setting. It is an interesting mix of smooth acceleration lifting the front at small throttle settings coming out of the corners. It rips right thru the mid-range and revs hard on top.

This really feels smooth and seamless with the same acceleration, maybe more!. Has a feeling like it would make for better lap times. Before I mentioned it feels like a Husa 501, now its a supercharged 501 :) .

I have now added an external screw to adjust the pump stroke at the linkage pivot, no disassembly required. So I tested back to back with the pump at 1mm stroke:

Adding the pump back was a little rich, turned the fuel screw back to 3/4 turn...

This feels close to the same, (it is about the same) but has a tiny improvement in the initial thrust on a quicker roll-on. It's almost splitting hairs, the pump adds some snap but makes it too rich. The richer clip #6 and pump fuel are at odds.

Back to back testing works well to compare. The non-APJ can be very close to with the APJ. There are drawbacks to each. The #6 clip would run rich on downhills and on deceleration at times, sputtering or popping. The pump is rich going on/off/on throttle in technical sections. Some leaning on the needle clip/or taper could balance this out as a compromise.

More to come- Adjustable PAJ was ordered last week and will arrive soon.


Taffy, I knew you were right that my test with only 1 clip (EK-#5) was an unfair test of a non-APJ. Just took some time to get there. With the addition of the APJ screw to stop the stroke early, I can now both start and stop the pump at desired throttle positions with simple external adjustments.

I have found that extremely short pump strokes need to have a little more delay so the pump can refill at 1/8 throttle. If it doesn't refill, the pump can't deliver for the next throttle twist.


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

just got back from the pub JD

that's wonderful news!!!

together i think we're going to crack it!

i think the flood gates are going to open now. i'm not really going to say much this time around (too pissed!) but i'm sure of one thing;

we won't settle for second best!

there's no hiding place, the winner will be there for all to see.

even if the answer is to have a little APJ i'm sure we're going to get there soon.

the next month is going to be very exciting i'm sure.


You two guys are like kids in a candy store :). This is actually quite exciting!

Right now, my bike is INCAPABLE of pulling 3rd gear wheelies. After stepping off of my CR250 Honda, which could pull 5th gear wheelies, this bike was a let down. I am glad it is a short matter of time before your goals have been achieved!!

Sorry I cannot contribute. I just struggle to make it through the day right now. If I can make you two or anybody else laugh or even a smidgen of a smile, I HAVE achieved my goal! :D

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