Jetting Qs

absolutely JD

i found a clear and discernable power surge when i did the cam timing and as i've said before you might (just might) be happy with the standard YZ inlet cam being 4D out but i defy anyone to say that 8D on the exhaust cam is acceptable.

it's been in the back of my mind for some time that the "Taff timing" is the only other change.

but isn't that the beauty of tuning? to change things in the right order inorder to go forward.

what if i hadn't had an 'M' needle?

what if i hadn't dropped the needle before i dropped the PJ?

if i hadn't dropped the APJ i would still be wandering around.


you've not relly given me much to go on have you! EKQ what clip? the other day you said you were at 800' now you're at 5,800'!

if your needle was above clip 1 you have actually lifted it compared to the EMP-c2, OK?

i would suggest that you drop the needle to clip 1 and then all you've actually changed is to make the bike leaner for starting and tickover. what exhaust have you?

i said that an ERM was what i was after so as to be on the middle clip.

james, have you noticed how lean they're able to make these 426's run?

the 37mm carb? i'm not going to buy one just to see if it works. i'll borrow one, report it here and if it's any better i'll report it here and you can add another $200 to the price (and thank me!).

but don't hold your breath!



i just went riding the other day @5800'.5800' is also the highest i have ridden this bike at.

i put the EKQ clip#4 just to see if it would be ok. i have not ridden EKQ @ a lower elevation. it is stock exhaust uncorked. i can not decide what exhaust to buy to put on this monster. i think if i find a stock YZ i will put that one on. i would like to find somthing quieter i found out how loud this thing is in the woods. WOW was i surprised. i had someone else ride my bike away from camp you could hear it a long way.

the ERM is on order i really want to find out how it does i am also going to get the ERN. i think the ERN will be the best bet.

i am also thinking of indexing my cams to see what the difference is. if it is anything like the normal production stuff for cars i am expecting to find it off at least 4.5deg. i an going to do both cams to see if there is more torque in there.(there usually is with other things i have done this on)



yz timed now

some mods

so you lifted the needle up three clips and also went to altitude. mmmmmm!

now you're going to index your cams before you get it running right. MMMMMM!

i would slow down, stop pissing about and do the job properly. your PJ is very rich compared to the PAJ so order a PJ42 while you're there.

you should have run EKQ clip 1, that's why you had a misfire at mid revs (i think!).

ERM or ERN? well you'll be able to tell us all pretty soon.


[This message has been edited by Taffy (edited October 20, 2001).]

i have a 42 in the box (all the way from 50to38) i am going to do the 42 for sure. i will do some more testing with the new needle and pilots on saturday. will keep you guys posted. on how it comes out.



yz timed now

some mods


if there's anymore to add after this post that IMPROVES the bike-it had better be good!

start line setting was

165 MJ

180 MAJ

needle EMM -c2

3/4 PAS (#85)

38 PJ

2 turns PS

taxed the bike first thing and went green laning so i had to be very choosy where i tested. the nice thing about having so few long strips was that i could check the low speed circuit on the mud 'n grass and the top speed stuff on the main roads that connected them.

i reduced the PS to 1.5 then 1 turn and noted how in almost a 500 rev "window" i detected a slight hesitancy so i dropped the PAS down to 5/8 (#75) and it disappeared. PS back to 1.5 turns.

i next tried the 160 MAJ and hit the road and it just went straight to the redline. you could almost feel (i say almost) yourself falling forward when the redline was reached.

on my bike nothing happens, you simply can't hear the revs going up anymore.

i next dropped the MJ to 160 and the roll on in top was improved.

i then changed the PJ to the 35 and that was it. pure nirvana. what you really notice is that where a week ago i would have ridden along with say 1/4" of throttle, yesterday i was riding with an 1/8" and the bike was running on with only a whiff of throttle.

it's probably hard to imagine. you simply don't open the throttle as far to go anywhere, i think it's because the bike doesn't need that "gap" between throttle whacked open and fuel moving. if a bike is rich, it "likes" that gap because it's only then that the mix ratio is correct. now it doesn't have it and doesn't want it.

i would put the hesitancy now, down to 2mm of the twistgrip and yes i can sit there at tickover and catch it out but otherwise it's just about perfection.

tests left? phew!! um?

well i have this 'F' needle (FMP)

i have a slide ready with a taller cutaway (2mm)instead of 1.5mm.

i have to wonder "if only they made a 32PJ" could anyone tell me if sudco reckon they do?

riding home it was hard to believe how far it had come and all the hard work has been worth it. each guess and each idea has been in the right direction virtually everytime with just the 3 month gap away from the bike making me pathetically forgetful of what i'd even done to it (thanks mate!)and don't mention the #140PAS!!!!.

just to recap

PS 2 > 1.5 > 1

PAJ 3/4 (#85) >5/8 (#75)PS back to 1.5

MAJ 180 > 160

MJ 165 > 160

PJ38 >35

when i got back in the yard i said to myself "i'z got to know" (name that film!) and dropped the needle just half a clip and had a light vibration so it was spot on at clip 2.


[This message has been edited by Taffy (edited October 20, 2001).]

Quoted from a surviving robber to Det. Harry

Callahan, San Francisco Police Dept. in "Dirty Harry" ? Just a guess from this side of the pond Taff.

Wow Taffy,

You have gone from one end of the spectrum to the other to piece this puzzle together without an accelerator pump. The custom cam and euro exhaust really clouded my vision of where you would end up. (Should we compare it to a DRZ?) Does your slide have a number stamped on the bottom indicating the cutaway? The EMM was the right move to get bottom end fuel with your smaller pilot jet.

Considering how well tuned it is with the EMM needle, the FHP may be lean off idle (tickover). Can you get a FHM too? I'm sure you get the picture.


Finally some time to do tests today.

Unbaffled US pipe only. All tests 158MJ and 42PJ. I Moved the PS all over for each needle setting (.5 turns to 2.5). When I mention sputtering below, it is all 1/4 throttle to about 3/4 constant revs and during slow roll-on of the throttle (just like always!). This sputtering is significant because during slower throttle roll-ons the bike gets uneven accelleration because of it. These are all the tests I had time to do. I need to try more positions on each needle, but I was attempting to go for what I've read that people are having luck with. Here goes:

EKQ Clip 2. Sputters about the same as Clip-3. Sputtering improves as I move the PS out. Got it out to about 2.5 turns and there was still some.

EMP Clip 2. Easier to kill the bike off idle, but adjusting PS helped this. No great difference noticed from the EKQ. Still sputters.

EMN clip 2. Starts good, runs good, still sputters. Again, largest reduction of sputter is with PS 1.5 or more out.

EMN clip 4. Starts good, mid and top are REALLY strong, I liked it! However, sputtering is the worst ever.

Just to see the effect, I turned the PS all the way in and found it to drop the idle speed, so it is doing *something*.

So, help me draw some conclusions from this. It is interesting that power is really good at EMN clip 4. Next I will try my other needles at other clip positions. Results say that clip 1 might fix it, but lower clip positions make better power. Does this make sense?

The results make me suspect that sputtering is related to the pilot circuit since turning the PS affects it somewhat, but the pilot ckt isn't really in play in the rpm range of the problem.

According to the pic's in my service manual, the jet needle, the MJ and the throttle valve cutaway are the dominant players in the rev range I've got trouble in. Specifically, it says that rough running is due to a rich condition, so this supports moving the clip to the top.



If EMP#2 sputters from being rich, there is probably something wrong elsewhere. frown.gif

The EMN#4 or EKQ#3 are both close to where most riders end up. The strong mid range is what you should expect. If you have a chance, try a #165(+/-) main to see if wide open throttle is better.


Thanks James,

I am going after the main next. Since the problem doesn't exist with a restrictive pipe, and the needle stops affecting the problem at about clip 1-2, that's about all that it really could be. Based on Taffy's results, I bought a 160MJ. So I'll start trying small things here to see what influences the problem.

Another thought on changing the MH is that scott in KC has now fixed this problem, and he is only 3,000 feet different in altitude than me. The only difference between his bike and mine is he has a 170MJ vs my 158, and he does have a YZ pipe.

If I can't get the US pipe to work, EMN-4 with the Europipe might just be the ticket.


[This message has been edited by Stefe9999 (edited October 21, 2001).]

blue thunder

spot on! you're a bloody star! was that a young danny glover?


c'mon JD! look at all these 426's running a 42PJ and what about Hick? he says nothing, just quietly gets on with it (40/38pj AND A yz PIPE).

the FHP i sent back and i wish now that i hadn't ordered an FMP, FMM yes!


your jetting is unbalanced. did you read recently that i said that the MJ almost controls the needle. the reason your needle is on the 4th clip is because you're not letting it have enough MJ.

have you done any high speed runs on the road? c'mon man.

at least a 165/168MJ until you go to the MAJ's suggested above.

your first run with a larger MJ will be awful until the highest revs OK? BUT DON'T WUSS OUT. drop the needle not just once but twice.

you're PILOT AIR JET is causing the low end misfire. why do i know?

now read really carefully.

the PS tweaked right out is a richening screw. no matter what crazy PJ's and PAJ's are in there, IF IT'S WOUND OUT AND IT'S BETTER IT NEEDED MORE JUICE. OK?

but don't follow the lemmings over the cliff. you're whacking in tons of air (PAJ)and have only a baby, baby PJ(42). get that air # down to balance out the PJ. with a 42 i was running 3/4 turn of PAS which is #85PAJ.

you've got a chioce which everyone except hick and i have done since this site's inception. you either go up to a 45/48PJ and kiss the low speed acceleration goodbye or you get your PAJ #'s down. then when the two are balanced out you will find that the much sought after (and by now nearly legendary) 1.5 turns of the PS CAN BE DONE.


BTW everyone

i've put pretty much all the recent jetting mods that i've done on this thread you can find my first experiments and some embarrasing hug-hug kissy-kissy (taff had been down the pub!) on "snap......" and then later "more snap....." if you put these into search and "Taffy" as the name you'll be there i hope. (WR400/426 search only)

JD i've still of course to check that a 170 MAJ isn't the right one AND i've got to do some proper MJ tests all over again!

finally, if you look above at all previous posts you will hear very little about popping under deceleration. this is because nobody else has sussed that it's the balance between you're PAJ/PJ that is more important than what the numbers are.

i didn't hang around long enough to find out at the 48/45 end but it also didn't seem to be too critical. all the below should give you a 1.5PS.

48PJ 100PAJ

45PJ 100PAJ

42PJ 85PAJ

40PJ 85PAJ

38PJ 75PAJ

35PJ 75PAJ

you try these combo's stefe and stick with your euro pipe WHICH YOU SAID YOU WOULD and you'll hopefully get some great results too.



I am going back to run the tests on the Europipe, I was just *DETERMINED* to make the US thing work. I've come to the conclusion that an unbaffled US pipe is TOO free flowing for any carb components I have. At this point I believe that a large MJ (170 or so) would probably fix it. But, enough of that.

I like your explanation of the balance between the PAJ and PJ, its the ratio between them that matters.

I'm going to do all the tests again with the Europipe and re-post. It might be up to two weeks before I can ride! :-(. In the mean time, I'll get a few new bits ordered.

In the mean time, help me understand a couple things so I order the right stuff.

1. PAS is an adjustable PAJ right? Don't have that. Since I prefer trail riding, I'll go with the 42PJ/85PAJ so I don't loose low end. Any idea what the stock Euro PAJ is?

2. Which MAJ # above you are referring to that I should reduce to 180 or 160?

This sounds like the best input yet.



I think I've given up on the US pipe. I am going to try one more experiment with it however, I made a restricted orifice that fits into it with an opening 1 1/8" diameter.

[This message has been edited by Stefe9999 (edited October 21, 2001).]


the std wr99 PAJ was a #75 but yamaha have been to #100 and back. get the PAS you'll never need another.

yes a 160 or 170 MAJ based on my latest tests. the 160 was far better than the 180. i would go for the 160MAJ.

what do you mean by lose the bottom end?

the lower my PAJ/PJ combo's have gone the better it has run. yours is halfway so that sounds fair.

stick at one pipe stefe. you won't regret it. i just don't think your minds on the job sometimes...



The #42 pilot with #75 pilot air and 1 1/2 turns out was far too lean on my WR. The pilots screw needed to be turned out 3-4 turns.

Only after installing a #45 was it even close to acceptable. #45/75/1 1/2 turns was an excellent setting. The #45/100/ 1 1/2 had running on and irregular speed idle. The piot screw needed more turns out and lacked torque.

The #48 pilot was best with a #100-#125 pilot air jet. The pilot screw was only 3/4 - 1 1/4 turns out. This gave easy starting, great- smooth torque from idle, and no stalling at extremely low speeds.

A #50 pilot jet was too rich.

These tests were done mostly with EMP/EMN needles. The last letter (straight diameter) becomes important in this area because of the small overlap.

So, my results aren't the same as yours and those other bikes running a #42 or smaller pilot jets. Whether from elevation, temps, cam timing, exhausts, or whatever reasons each of us has some variation. I make my suggestions based on the majority of where riders are having problems and on my own test results. These are just estimates. They aren't going to be perfect for everyone.



i believe they're validb tests. i see it as going down a corridor that has a thicket of thorns on the left and right. i've been able to keep going by being lucky and notgetting 'tangled'.

i only disagree with three of you on the MAJ tests!!! well i do like to stack the odds against me!

nobody has disconnected their APJ and used the _ _M needle except me.

i haven't tried this open exhaust yet. everyone yesterday was being DB tested and the WR euro pipe is the only one bar the XR pipe's that they just wave through.

you're forgetting a whole host of things. the needle is really low which leans off the 1/8-1/4 area as well.

this is what i have left to test.

main jet to go with the 160MAJ. (it might want a 170 but i'm happy at present with it).

if i lean the MJ the needle may need to come up 1/2 clip.

the old DXM needle will be tested on clip 6, 7, 8 to see whether i can get any snap back from a SS.

i will also try and swop the FMP for an FMM needle. i may even of course consider the FRM (if they do one like it or close)

having got some snap as well as using your needle charts i may attempt to make a 'special' or at least get simon my engineer to have a crack at it.

the 2.95 and 2.99mm reams were a waste of money (as we stand) as was the EKT and EKX needle. the 2mm slide cutaway done only last week would seem a waste. we'll see.

you still haven't explained hicks bike!


[This message has been edited by Taffy (edited October 22, 2001).]


Hick rides anywhere from 4000-8000ft elev. and in warmer temperatures. A #38 to #40 in summer is not that much different. He mentioned using a #42 at 4000ft in winter using the PAS= #85 versus my #45/PAJ= #75 at sea level and 60F. At the same time he's talking about using EJP#4 in winter, richer on the taper than EMP#4-5 or EMN#4-5. Things start to even out.

I only ran the EMN without the APJ. I tested EML and EMM nerly that way with very little pump stroke. (thanks to taking good notes smile.gif The EML and EMM probably would have been better with a smaller pilot jet and were never tested in-depth. When a bike is running great it's hard to get motivated to create a problem and then search for an alternate way to make it better. The EMM and FHM were left up to you. wink.gif


can't agree JD

you've stretched the point more than bill clinton's pant elastic!

HIck runs a 38 or 40PJ not a 42. he runs EJP c3 which is 1.5 clips below EKPc4. he does all this with a _ _P needle.

isn't warm weather associated with high pressure normally?MMMMMM!

his air jet isn't worth pontificating about.

we don't have many deep vained jetting petrolheads left on here but i would mark him and boit as two of them. no offence to anyone else ya'll hear now!

if he was running an EJM he would be on a 35/38PJ max and you know it.

two weeks ago i made a concerted effort to get about three 426 riders to try things and one or two others and at the moment the only thing that's been produced is a baby!

i'm not dreaming this stuff up, i'll just have to be patient and wait for the right person to try the right jets in the right order at the right time!

the MAJ tests were wrong and i'll wait for someone else to confirm. it took me 6 hours to collate the fact that what i wanted to believe wasn't true.

it's not a problem, my mistakes are public and so are yours. i'm not here to sell anything and the very people that some lads have listened to are. yet they gave little away to this a site that is dedicated to the owner.

in england they just wouldn't get away with it. i might be in the minority over here, but a berk selling suspension is a berk selling suspension, and on our web site!

now i don't believe you about the bike running so well bit! if you still owned your bike you'd still be testing, you couldn't leave it alone you old bugger!

no worries


[ November 02, 2001: Message edited by: Taffy ]

I’m amazed (and a little frightened) that either of you pay attention to what I run. I was quiet for a long time about what my bike liked because not many guys run at such high elevations in such hot weather, and so not many have experienced the significance (which is large) first hand.

The only time my bike really liked a 42 pilot was back when I still had the stock EKR in my ’00 YZ, and then I switched to a 40 in the summer (as I remember it, anyway). I may have posted my jetting at some point as a 42 pilot and EKQ or EKR, but I didn’t stay there for long. I was EKP-4 and 40 for the most part.

My ’01 has always had a relatively restrictive FMF Q (until yest. when it fell apart halfway through a race) and of course the EJP-3 and a 40 pilot since I’ve owned it. I ditched the 42 right away.

The point is this isn’t apples to apples.

I think that elevation combined with high temps. is a huge factor. I’ve NEVER seen a bike (car, jet ski, boat...) here that didn’t benefit, somewhere, from leaner jetting. Holley, Edelbrock (the green step-up springs are the hot ticket), Carter, Mikuni, Keihin, never, so I probably wouldn’t recognize a lean condition if it crawled in my shirt.

Just so you know, that is my two Rupees...

How embarrassing.

I just read (again, I hope) my second post to this thread, made 9/26, and it is a not quite verbatim, but close, copy of what I just posted a few minutes ago.

Going on 100 posts, this thing has now come full circle (you are welcome).

Boy am I glad that I can be such a helpful guy.... rolleyes.gif

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