Jetting Qs

244 replies to this topic
  • James_Dean

Posted October 22, 2001 - 09:02 PM

Yes, if the WR were still in the garage, I would still be hunting for that last 2%. --Maybe with an FHM needle and 45 pilot.

A quick search brings up a lot, and now I see you have stayed with the 40 pilot. Posted Image

EJP#3 is 1/2 clip richer than EKP#3. Makes EJP#3 1/2 clip leaner than EKP#4.

Needle EJP#3=EMP#4.5 is what I would consider a very rich clip position for 8000ft elev and 80F+ unless a smaller pilot jet and a reduced APJ is used. So Hick runs a 40. While usually I'm at 500ft and 50-60F running a 48/100-125 PAJ and never letting the pilot screw get past 1 1/4. This is 3 pilot circuit variables and 2 needle variables all piled together at 0-1/4 throttle. Having fun? Posted Image I've tweaked them all, but emphasized differently than you and the results aren't the same. Each has a characteristic of it's own and I chose them for my riding style and conditions. Not for everyone else.

My original postings on needles a year ago was aimed at mass appeal, trying to make a general setting, which looking back was less than ideal. I could have just said run what I run and nothing else but that wouldn't have been right for the high altitude riders. So over time you see more and more of the uncensored conclusions. It fits some riders and some bikes better than others.

The other consideration we have skipped here is the discussions of "Woody426" about the "air cut valve". This is claimed to be bypassing extra air and making lean hanging idle conditions on some bikes - WR's only. Just one more thing on the pile, 2-strokes seem so much simpler.

James Posted Image

[This message has been edited by James Dean (edited October 23, 2001).]

  • neWRiver

Posted October 23, 2001 - 07:43 AM

Originally posted by James Dean:
The other consideration we have skipped here is the discussions of "Woody426" about the "air cut valve". This is claimed to be bypassing extra air and making lean hanging idle conditions on some bikes - WR's only. Just one more thing on the pile, 2-strokes seem so much simpler.

Right on JD. That is the most relevant statement made on this thread (based on the original post). Thanks for getting this discussion back on track. I'm a dirt bike newbie and I appreciate the knowledge and experiences that you have shared on this board immensely. Although I'm nowhere near "hunting for that last 2%," I have learned alot from your posts and can honestly say that I understand the fundamentals of carb jetting to a much greater extent than would otherwise have been possible. Contributions from straight shooters like Hick are also priceless.

I have been stuck in my jetting efforts on this very same issue. It seems like this ACV and neutral wire issue may slide everything into place and I can start doing some real "performance" tuning from all that I have learned here. Posted Image

[This message has been edited by neWRiver (edited October 23, 2001).]

  • Taffy

Posted October 26, 2001 - 11:10 PM


you're a newbie. so sit down and be quiet, there's a good boy.


i broke my rule of only talking about the needle and not the clips and paid for it! and did i! you could have said that EJP4 and EKP3 are 1.5 clips apart IN THE OTHER DIRECTION! that's all it needed.

anyway, you're obviously feeling the pressure. what used to be a known fact, inside of 6 months has become second guessing. fancy getting a 2-smoke katoom and then spending all your time on this web site still!

get another one JD. i want to get a YZ426 and change 1,2, 4 and 5th gears. i can't see why others can't be arsed, guess it will be left to the old 'viet gwent' himself again! never mind!

i've just taken stock this morning of a 165 and 170 MAJ so i a little session on top end jetting is immenent. as you know the needle is only 1/2 up on being lean so if my MJ does go to 155 the needle will have to go up. as stated previously, the MJ holds a tight grip on the needle.

your hawiaan friend had an open pipe otherwise he would be very similar to mine perhaps. a 155MJ is just around the corner. and THEN i'll put the 'F' needle in!

also from Allen's this morning are two needles.

DMM for snap and taper start tests only.

FMN for all that top end stuff you've been telling me about. as you'll have spotted in your catalogue, i could have had a FMN or FMP but NOT a FMM!

it was easy to work out which way to go. as i've told you, the start and tickover are lovely/tad rich maybe. so an 'N' is good.

but the other benefit i'm looking for is a very slight drop in richness at 1/4 throttle, after all i am on the lowest PJ (35)they do.

my usual ebulliant self got my a factory stock ordering photocopy from Allen's with the underlined exclamation "as you can see Keihin DON'T make a 32!". only a yellow card this time!

so an FMN with 38 or 35 PJ will suit me fine.

may not ride at all today/tomorrow as i have stacks to do.

so it's 'D' for snap wheelies, 'F' for top end. you await with baited breath mon ami?

i can sense that personal needle grind isn't far away.


  • James_Dean

Posted October 27, 2001 - 09:28 PM

The taper start location is important, FHM and FML are in the options. If you graph and compare, the tapers start close to the same on FHM and EMM. EMM#2 has a taper start close to FMN#4. Suppose you already knew.

Wish you would jump over to a more open exhaust like the majority of the forum riders. It would be interesting to see which way the change leads you. The open exhaust on the 400/426's and the 250F's is where I see the F taper needles working best.

  • neWRiver

Posted October 27, 2001 - 10:19 PM

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:<HR>Originally posted by Taffy:

you're a newbie. so sit down and be quiet, there's a good boy.

Sorry, Taffy. Can't oblige. I don't want to be your "good boy". :)

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:<HR>Originally posted by Taffy:
you await with baited breath mon ami?

Are you for real?

Do you honestly feel that somehow you are so much more significant that others can only strive to compromise the wisdom of your rantings?

Or perhaps you wish only private audience with your faithful (and heretofore silent) followers. You ought to write a book.

I, too, am sensing that you are very close to a personal grind. I think you should reevaluate and get out and ride more instead.

  • Taffy

Posted October 27, 2001 - 10:50 PM


you've posed an interesting question? clip 4 as a start it will be, Ta!

but i'm presuming that the lower end of the needle will be the fulcrum that i can work around. i'm hoping that at most i'll need a 38PJ, that the low end will work the same and that i'll have a blast at 3/4 throttle/4th and 5th gear roll on?

the top end MAJ/MJ will be fun. a good needle should be a good needle regardless of whether i'm running a restricted pipe. but theory is one thing...

we'll see


  • Taffy

Posted October 29, 2001 - 02:17 PM


i've just used your charts for the first time and they're excellent, no better than that, superb.

well done and a big thank you again. having placed FMN clip 3 next to EMM clip 2 i get a lower taper start, they cross over roughly where you want the needle straight to at 5/8-3/4 throttle. then you get the narrower portion at the tip which is hopefully going to make it go.

the lower taper start i hope will mean a higher pilot jet will be required but at 35PJ the bike is presently at it's best.

so i want to come back into the PJ sphere.

i am designating wednesday for a bit of fun as we are coming to the quietest time of year for me at the present.

this weekend i have my last meeting with the club that does the DB tests so it will be nice to have it humming on the 'F' this weekend.

after that it's two weeks to the big national that is coming this way; the john banks enduro. in that fortnight i would like at some point to try the open pipe.


  • Taffy

Posted October 31, 2001 - 11:40 AM

winter is really here! did a squelchy ride today and didn't do a great deal to it. all the same, i managed to hit all the right buttons.

start; MJ 160, MAJ 160, EMMc2, 35PJ, 75PAS, 1.5 PS.

tried 155MJ

the bike shot from low to high and felt vibrationless. revved clean out, but popped on the overrun for the first time in a long time top to bottom on the decel. in all a big improvement.

went up 1/2 a clip and it was great at the top of decel not the bottom.

PAJ 75>70
noticed a 500/1000 rev window at low revs where it vibrated a bit so i tried turning the PAS in to just a smidgen over 1/2 a turn which is 65/70PAJ. improvement. found the PAS at 3/4 turn, don't ask how it got there! mind you, you could only feel it trail riding and would never have noticed it if i'd been ripping it up. no pop on decel.

first time i've pulled 'little one's' in second without yanking or leaning back.

left to do?
lower MJ?
snap tests by lifting various needles right up and playing about.

sorry i didn't get on to the FMN.


  • James_Dean

Posted October 31, 2001 - 12:31 PM

Thanks for the update, still checking in and find it interesting.


  • Taffy

Posted November 03, 2001 - 03:26 PM


just went for another green lane dabble today and kind of didn't change much but painted in a new area of the picture, if you know what i mean.

those of you who have read the above posts will know that i pre-guessed which way the jetting would go on wednesday and it did. also that the "SNAP" from zero that i had in february/march was the result of an exceptionally high taper start. we're talking EKP clip 7 (yep, i said seven) sadly i could not jet around this needle setting and so i had to give it up (but NOT forget!).

when on wednesday i put the needle up just 1/2 a clip it was the first upshift of the needle in over 90 meticulous back-to-back tests.

this got rid of the backfire on decel at high revs but not lower revs.

and today?

by going to a 160MAJ i was then able to lower the MJ from 160 to 155. i could feel a real improvement which tell's me it was badly needed and that there is room for it to go down further to say a 150MJ i would think.

as i've also stated, the MJ controls the needle "under house arrest" and as the Patrick Burns report also states (and i concur) the MJ works down to idle (tickover).

so when i dropped the MJ from 160 to 155 i rightfully put the needle up 1/2 a clip. i also today did the following tests and i hope you'll see how this part of the picture is starting to unfold.

start set up
bike now pops on decel at low revs (top end has been sorted by going plus 1/2 clip). 155MJ, 160MAJ, EMM clip 2.5, 35PJ, 70PAJ, 1.5PS.

test 1
tried PS at 2 turns and 1 and it was no better.

test 2
dropped PAS to 1/2 turn which is PAJ65.

lot better feel but still pops back on decel. conclusion? leaning off the MJ has affected the pilot circuit!!!

test 3
lift the needle from 2.5 to clip 3 even though it doesn't appear to actually need it.

bike has virtually stopped popping on decel. since wednesday some of the snap is coming back.

next step i see as being;
150MJ will be good.
needle up .5, 1 or 1.5 clips=more snap!
if i need the 38PJ i'll get it.

a week ago i'd have said that my jetting was 90% perfect bar the lack of snap. looks like i may be able to dial the snap back in!

keep you posted.


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  • LarryCO

Posted November 05, 2001 - 06:42 AM

I purchased a Pilot Air Screw setup this past week and installed it over the weekend. During my jetting trials, I was receiving strange results based on different settings of the PAS. Can you confirm the following for me?

1. Screwing the PAS all the way in (snug) effectively shuts all pilot circuit air off. Measurements of the compatable PAJ are made by the number of turns OUT from this position.

2. 1/2 turn out = 75PAJ
3. 3/4 turns out = 85PAJ
4. 1 turn out = 100PAJ
5. 1 1/2 turns out = 125PAJ

If this is the case, I sure was receiving different results between the use of a 1/2 turn PAS and a normal 75PAJ...


  • Taffy

Posted November 05, 2001 - 12:08 PM


did you read the patrick burns write up? halfway through he has a full chart of the values of the PAS compared to the PAJ that it replaces. and larry you've got your figures wrong.

1/4 turn out from closed = 45PAJ equivelant.

3/8 = 55PAJ
1/2 = 65PAJ (note larry)
5/8 = 75PAJ
3/4 = 85PAJ
7/8 = 95PAJ
1 = 100PAJ
1 1/8 = 110PAJ
1 1/4 = 120PAJ
1 1/2 = 125PAJ

your problem larry is that your needle straight is far bigger than mine and this is worth, i dunno, maybe 20% of your tickover mix. on your thread i've asked you to describe your starting symptoms and this will help me give an opinion from 6,000 miles away whether you need a narrower needle straight. i.e. not an R, not a Q, not even a P but possibly a N or a M needle.


  • tbronco

Posted November 05, 2001 - 04:40 PM

Taffy, could you explain to me what the benefit of running the rich (narrow)needle straight/ (small)lean pilot jet?
Is it all because of the position of the taper start?

  • Taffy

Posted November 06, 2001 - 12:09 AM


the straight bit helps you go about 3 yards, then you're on the pilot circuit. the lower the PJ/PAJ the sharper the response of the bike.

it's not rich, it's fine. even good 'ol JD has gone from recommending the EKP outright to EKP altitude and EKN at see level. that's one letter from me.

i know that he sold his bike when a considerable amount of testing was left for him in this area.

JD specialises in helping people set up bikes from what they have, even though as the irishman said to the lost american in county donnagal; "well toi be sure sir, if i wanted to be getting to limmerick i whouldn't be starthin from heare"!

i just want to race them. luckily i need the same thing as you

no stalling
instant response
no vice's or glitches
top end
excellent fuel economy

i was chatting with a XR4 runner and i started the 1 1/2 hour afternoon session with the fuel above the lower screw and visible through the opaque tank. "you're not going to race with that in there are you?"

six pints in 1 1/2 hours i'd used in the morning.

the needle taper start can't really be chosen. it chooses itself i'm afraid. as you can tell from what, 200 posts on "snap..." and "more snap..." plus this thread.

you get the needle straight right, you get the clip position right and then after that you pray!

the taper start can't be felt as such because you pull on the throttle and the taper flies out the hole. thing is-you've just wrenched the throttle, what, 40mm in .02 seconds!

what i do know is that the nearer to the highest setting you can run the needle the "snappier" it will be.


  • LarryCO

Posted November 06, 2001 - 06:22 AM

I figured that the E series needle was the cause of my excitement last weekend. Once I get my jetting down, I'll swap out the equivalent D series needle to feel the difference based just on the jet needle taper.

Didnt have a chance to read that article yet (meltdown here at work)...I appreciate the PAS setting corrections. They pretty much explain my problems/confusion this past weekend...

Regarding my current idle/choke condition at 45PJ/75PAJ/1 turn, it's not running rough at a warmed-up idle, but it's easy to get it to do such by going to 1.5+ turns...and I cant get a lean condition by turning the PScrew all the way in. Also, cant start the bike cold by using the choke...have to start it by using the hotstart. Finally, there's still a bog at the low end when opening up the throttle from a standstill, although no where close to where it was prior to the BK mod.

Given that, your advice, and my newfound understanding of the PScrew and the effect of the straight jet needle diameter on the low end, I'm ordering a 40PJ, E_P, and a E_N today. I plan on trying the following: 42PJ/85PAS/EJQ, 40PJ/75PAS/EJQ, 40PJ/75PAS/E_P, and 40PJ/75PAS/E_N. Any other suggestions?

Thanks for everything guys!

  • Scott_in_KC

Posted November 06, 2001 - 08:08 AM

it's not running rough at a warmed-up idle, but it's easy to get it to do such by going to 1.5+ turns...and I cant get a lean condition by turning the PScrew all the way in. Also, cant start the bike cold by using the choke...have to start it by using the hotstart.

Ditto Larry! I'm at 1000' with the settings below. With the ACV mod, at 42/75 pilot, I'm experiencing the exact same symptoms. I pull the hotstart halfway when it's running and gets crisp. Still getting a slight burble at constant so going to clip #2 first off and following taffys lead that the needle is affecting my idle mixture quite a bit more than I would have ever imagined.

  • LarryCO

Posted November 06, 2001 - 08:27 AM


I'm starting to get pissed off here...talking with Sudco and a couple of the dealers here in the Denver area. No one even recognizes the existence of an EKP, EKN, or an EKQ needle. However, many of you out there in TV land are frequently referring to your use of these jet needles.

I know there's parts microfiche problems with Yamaha, but can anyone out there tell me what the real Yamaha part numbers are for these three needles? And a fairly competent dealer phone number to call to order them? How about a part number for a jet needle close to say a DVP (with the D_P being the significant criteria)?

I'm getting tired of the whiny girl on the other end of the phone telling me I'm stupid...which I may be...but I'm still getting tired of it! :)

  • Taffy

Posted November 06, 2001 - 11:31 AM

from yamaha
EKN is part #5jg-14916-en
ELN is part #5nl-14916-en
from sudco
the EMM is an off the shelf needle. N427OCEMM (017-261)

now i've said nothing about the ACV because you may think i just spoil for an argument, but at least with the engine back-popping you could tell if you were in a lean condition. what are you going to do now?

you need all the help you can get to get the jetting right and you've just taken away about the only audible sound going.

don't listen to any of that **** about screwing it all the way in and it dies blah, blah. it's only ever happened to me once when i got it slightly wrong.

how long have you had the **Q needle in? i don't want to know about your warm start or what it did with the old needle. just the **Q needle from cold. the revs, what do they do?

i would change the needle first to a **P then to the **N. same clip. do not do two experiments in one here. then your PC.

also don't go down on the PAJ until you need to, so go down on the PJ's first and fiddle with the PS to get the snap right. change the PAS when you feel it "vibrate" instead of reacting.


  • James_Dean

Posted November 06, 2001 - 11:49 AM

Part numbers were correct in the '00YZ426 service manual only-

OBEKN P/N 5JG-14916-EN
OBEKP P/N 5JG-14916-EP
OBEKQ P/N 5JG-14916-E1 (NOT EQ)

The newer '01YZ250F has needles which shift the clip position by only 1/2 clip and are correct in the fiche.(EKN#3=ELN#3.5, EKP#3=ELP#3.5)

OBELM P/N 5NL-14916-EM
OBELN P/N 5NL-14916-EN

ONLY Yamaha will have the OBxxx needles listed above. They are a hard coated/plated aluminum.

Sudco ONLY has OCxxx, brass needles, which are less expensive (~$8). These are another 1/2 clip leaner. (EKN#3=ELN#3.5=EMN#4)


Hope this helps,


  • LarryCO

Posted November 06, 2001 - 12:48 PM

Thank you! You've probably saved me hours of arguing with the dealer folks over part numbers. Beers on me if you're ever in Denver...

I'm following your instructions regarding the E_P and E_N needles. Probably wont be in this weekend, so I'll be using my new EJQ needle I just put in this past weekend. I'll most likely go back down and try the 42PJ and 40PJ at a 75PAS, monkey around with the PScrew for both, and call it a day.

Thanks once again!


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