Don't know if I expect much from the BK

I did the mod last night, will ride this weekend. Pre-mod, the squirt was only about 2 seconds. According to what I've read, this is way less than usual. I assume you measure the duration by quickly opening the throttle, not a slow roll-on. My drill/tap set was $4.49 at H-Depot! UGH!

My bike never bogged at the bottom anyway, so I don't know if I'll see much of a performance difference. Should I expect to have to richen up after this (needle height)?


01 WR426, uncorked stock pipe, sometimes Euro pipe, EKQ POS#3, #158 MJ, #42 PJ, 1 3/4 turns.


i could pull my hair out with you i really could. i've explained everything in finite detail and yet...

your running 7 less MJ than me

your running 2 clips richer needle than me

your 1 PJ richer than me

you have an accelerator pump pouring in fuel and i don't.

do you need to go up on the needle when it's the pilot circuit that is affected?



Taffy, for ANY particular jetting specs on an individual bike, shouldn't you see SOME difference by doing the mod? i didn't & therefore was completely underwhelmed & can't figure the fuss.

in general, mine's a 2000 W/airbox off, throttle stop trimmed, 178mj, 48pj, stock clip 1 notch richer & an add'l 1/4-1/2 turn on the screw @ 1100'. the bike runs absolutely fantastic since the day i dialed in & i haven't touched it yet. the GW mod had no effect whatsoever, so i've been confused. any thoughts?



nah! it's just me, sorry mate i just get a little you know...frustrated. it's like leading a jersey cow that's only got three good legs, you know?

i must be the only bloke left in the world who would say "i'll have a go at the whole hog" yep, copy the lot and see!

there are going to be some jetting charts put up pretty soon and i think they're going to be wrong. i think we've been sold a pup for the first two years that this site has run.

i can't say a lot more because i'll offend.

i've got very little time left to get a few of the new one's to change and have a go. the EKP clip 4 is still being recommended but already some of you are dead happy with EMP clip 2 etc.

this is 3 clips lower and i'm glad you found it. but it's like watching lemmings falling over plug foul cliff and not being able to do anything about it.

i need someone to try my settings quickly!! and his name begins with S and ends with E!!

as for you bob! you silly bugger! i was serious about the exhaust pipe in the petrol tank!

it's an old trick. you run the car for ten minutes IN THE DRIVE (i'd better make it absolutely clear; STOOD STILL)exhaust fumes are an inert gas my friend, OK?

isle of man 1992, cracked tank discovered at 4pm, welded at 5pm out to practice at 6.15pm. sorted. if i had the balls to put it on my exhaust, what did the welder have?

anyway i can't blame you for thinking it was a leg puller!

i'll take you to jetting heaven gentleman but do try and keep up at the rear!


Stef999 & Boxterboy & Taffy,

Stef - First it is my impression that the better your bike runs the less the BK mod helps. As I have tweeked the bike, each mod has done less and less, but has been more of a refinement. My impression of the BK mod is that there was too much fuel going into the engine when the bike was transitioning off the idle circuit and through the needle. My squirt was about 3 seconds long, this is a long time and it affects lots of different circuits.

Here are my too complaints about the carburation before the BK mod. The throttle seemed a little touchy off idle, difficult to control during slow 1st & 2nd gear turns, especially at the end of 45 minute moto when my hands got a little tired. The bike felt "too touchy" to small throttle inputs. The second complaint was one that I rarely noticed because the squirt was soo long. On a long uphill section I noticed that after the 3 second sqirt was gone, it seemed like the bike fell flat on power, because the hill kept me on the needle and without the squirt the needle was too lean.

Now after the mod, the off idle contol is much better and the mid range (needle) feels much meatier. I may even consider going to a 175 main from a 172 now.


You need to go up one clip (higher number, richer) on the needle, James Dean pointed this out to me right after did the mod. The bike flat died everytime I wacked open the throttle, one clip richer and the problem was solved.


I have to honestly say that your I just don't get your carb settings, They seem wwwwwaaaaaaayyyyyyyy !!!!!! too lean, I think you are way up in altitude correct? But I have tried going down in size on the pilot to a 45 per your suggestions and the bike is just dying for more fuel. Never have I fouled a plug, and my bike starts like a charm every time, and rarely do I have to use the hot start button.

So I don't know how you do it, (get your bike to run on such a lean mixture), Maybe it has a lot to do with my very open free flowing exhaust. But my experience says that my bike wouldn't even run if I got halfway to your settings.


2000WR - EKN#5, 172MJ, 226MAJ, MAJ Passage drilled to 278, 48PJ, 100PAJ, YZ timing, BK mod, 3/4 turn pilot screw, DSP tapered header and pipe, IMS tank & YZ seat, Scotts dampener & triple clamp & Renthal Fatbar 971, White Bros suspension, Dunlop 756's.


Hope you had a chance to have some warm beer last night! (I did) I think there is a good chance I've simply got a great running bike but just haven't ridden a mis-jetted one to compare it to. Hence, I've made an invite to other 426'ers to come up to the local track to compare.

Hopefully I will explain myself well enough here that I can put this subject to rest. My original goal was to make get my motor to run smoothly with the unbaffled stock US pipe, which it does not. If I could get this jetting right, I might feel good about getting a hi-performance muffler like a stroker SX1.

So, I'd like to help you in terms of giving you feedback on your recommendations by making the some changes you are requesting, but I've lost track of what you want me to change. Above, you mention being 7 lower MJ, but last time we talked you were at 160 and liking it (I'm 158). I am 2 clips richer than you, but I have a fatter needle straight. Clip positions I can change, but I think you are suggesting the EKP needle because you think my Q is too lean.

Before I go ahead with this, please answer two questions.

1. Are these numbers/sizes correct for riding at elevations from 4K-8K'

2. Are these changes targeted at making my US pipe work or towards enhancing performance with the Euro or both?

Hick recommended the EKQ to me, he rides at similar altitudes.

Also, I see you are going to a Stroker muffler. I thought you liked the Euro? I used to run one on my old Kawasaki, it is a great pipe, but a bit on the loud side. I've considered it for the 426 too, the quality was very good.


-Stef if you want to talk more directly.


We will definitely be able to compare notes at Berthoud.

when are we going to see fuel injection on these stupid things! carburettors are a pain, no doubt about it.

i have programmable aftermarket fuel injection in my car and to adjust the acc pump is simply a matter of picking up the handset, find the correct menu and then press ok. from here i can adjust the extra amount of fuel to be added (0 to +255%) and for how long (number of injector pulse widths). how great would it be if these came equipped with EFI. you could ride your bike while making these adjustments until the flat spot problem is solved. the tuning could be done spot on by the use of a dyno and EGO sensor, and the management will automatically compensate for cool days (air temp sensor) and for higher altitudes (atmospheric pressure sensor).

when will Yamaha take the next step? i want to stay with team blue all the way!

I'm in the same boat. I did the BK mod and my bike bogs and stalls when I grab a fist full of throttle. I have to roll it on.

My carb is stock, except for the throttle stop and grey wire clipped. Also did the intake and exhust fix.

I did how ever turn the timing screw a 1/2 turn clockwise with no help. Then I put it back and adjusted my bk mod screw all the way out and still bogs. Im starting to think it might be the grey wire.

The only thing I can think of is maybe the squirt isn't timed correctly when the slide starts to opens and the delay is whats causing it.

Anyway... I might take it to the shop (yes my wife almost fell over when she heard me say that. I have done over 10 top end rebuilds myself), but I figured I can have then adjust my valves, convert me to YZ timing, and then change out my needle if needed and get it right.


01 WR426 Uncorked, YZ throttle stop, Grey wire cut, BK mod. Do I dare change to YZ timing. (soon)


Are you frustrated because I've not changed to your jetting or because my bike runs pretty good with different jetting than yours? Jetting that maybe doesn't add up in your mind? I did the BK mainly because I believe that it simply delivers too much gas and others have liked the results.

I did not know that we are talking the pilot circuit here. You can bang the throttle open at any rpm and get a squirt. Keep in mind this carb tweaking is very new to me. If you can point me somewhere to learn the interaction between carb components it would be appreciated.



these bikes give out all kinds of false messages. time and time again what you thought isn't what happened. i came into this with quite a lot of experience but it's been hard work. first of all, yes you have an open pipe, and two, you have the APJ and i don't. so there are no cast iron gaurantees with this.

if you tried the 45 PJ did you kick out the PS as per my tests of 15 and 23 sept under jetting Q's?

if you had tried 45PJ/100PAJ with 1.5-2 PS you would have been ok.

have you got the PAS?

also while you're running the APJ at all it's possibly a waste of time because no matter how short the squirt it will always work in the middle of your pilot circuit.

you are 3 clips richer than mine. so although i have an M needle and you an N they restrict in the tube roughly the same because mine is right down and in it at clip 2 and yours is up and "out" at clip 5.


euro pipe


165 MJ as per "jetting Q's" latest (keep up at the rear!)

needle down once, and then again if good in 4th gear etc.

42PJ/ 90 PAS (7/8th of turn)

PS 1.5

no APJ

IMHO EKQ is too lean on the straight so try your EKP needle down.

my figures are to get your europipe running.


[This message has been edited by Taffy (edited October 12, 2001).]


When I tried the 45pj, I changed to the 75paj at the same time, and did increase the screw to about 1.5 -2 turns out.

With the 45/75 combo it runs OK, but feels a little weak. I am at 0' elevation. The bike felt like it would be good if I was at 4,000+ feet, or if I had a more restrictive exhaust. But the 48/100 combo just has more balls/meat/guts (whatever you blocks in England? call it).

I was riding at 8,000ft several weeks ago and the 48/100 combo and my jetting listed below worked fine. Only the EKN#5 felt a little rich. Other than that the bike started everytime and ran crisply off idle.

Today I even changed to a 175 main, since I think the 172 might be a little too lean. I don't doubt your results. As James said in so many words, the proof is in the pudding. And you are obviously getting good results, I just wonder why you can run so much leaner than anybody else. Is there that much difference in the exhausts? Usually an exhaust change might require 2 levels of adjustment. Like a 48 to a 42, but your way off the chart? You have lost me. Nothing personal, I am just not getting the results that you get.


2000WR - EKN#5, 172MJ, 226MAJ, MAJ Passage drilled to 278, 48PJ, 100PAJ, YZ timing, BK mod, 3/4 turn pilot screw, DSP tapered header and pipe, IMS tank & YZ seat, Scotts dampener & triple clamp & Renthal Fatbar 971, White Bros suspension, Dunlop 756's.


I had the same model and year bike as you with a YZ exhaust and everything you are saying about jetting matches mine exactly. A screen was installed as a spark arrestor part of the time which only needed a clip position leaner. Your results correspond so well that the comments are almost like reading from my notes.



The Euro pipe has about a 7/8" diameter opening and the unbaffled US is 1 3/4". When you double the diameter, you quadruple the flow. So this really might be the case. The europipe only produces 82Db and can not be modified at all.

Also, I have a very simple question, given a properly jetted bike at sea level, what is the SINGLE most common carberuation change to make to adjust for high altitude? Is it clip position, needle thickness, MJ, MAJ ...???

When I get my new needles in, I'll do testing with both pipes to help resolve this.



01 WR426, uncorked stock pipe, sometimes Euro pipe, EKQ POS#3, #158 MJ, #42 PJ, 1 3/4 turns.


it's difficult to compare over such big distances. i feel like coming over and saying "now look here..." but that wouldn't be the point and of course my settings really might not work for you.

the only thing that i can't make out is why Hick has gone off in a totally different direction to you and is running 38/40 PJ's and at altitude as well!

i was running a 45PJ/100PAJ then a 42PJ/100PAJ then a 40PJ/100PAJ before i finally knocked the PAJ down to #85. it then went 40PJ/85PAJ, 38PJ/85PAJ and at the moment that is where we stand.



I am using a DSP exhaust with a spark arrestor screen. At 8,000 ft (I am rarely at this altitude - but it is a good test to see where settings may be potentially too rich) the mid range of EKN#5 felt a little fat, but it ran great at 0 1/4 throttle and 3/4 to full throttle (w/ 172mj). So I was considering leaning out the needle. But as you remember when I did the BK mod the bike just flat died off idle with the EKN#4. So yesterday I tried an EKN setting of 4.5 with a washer, at the same time I went to the 175mj. With the EKN#4.5 and a 175mj cracking the throttle off idle was much better. It took quite an aggressive crack to get the bike to stall, where as at EKN#4 any amount of throttle off idle wanted to kill the motor. My question is, what should be changed to go to the EKN#4.5 and still keep throttle response crisp off idle? Just increase the durartion of the squirt? (currently set at about .3 seconds). Or Should I be looking at other needle options? Or it is totally unrealistic for my bike to carburate well at 8,000ft and 0 feet elevation, and I should just shut up and enjoy EKN#5 with my current settings. I am not opposed to experimenting. As always thanks for your experience.


Wow! That is a huge difference. I did not realize that the euro pipe has such a small outlet. My DSP pipe not only has a huge header, but it is also straight through. That may explains quite a bit.

As for what needs to be changed when at elevation, I am not aware of any hard and fast rules. James may have some insight on this. My guess is everything, but I have almost always personally been concerned first about my idle circuit. Because if this circuit is right, I will usually not foul plugs and won't get stuck deep in the woods.


Are you running at altitude and do you have a restrictive exhaust?


2000WR - EKN#5, 172MJ, 226MAJ, MAJ Passage drilled to 278, 48PJ, 100PAJ, YZ timing, BK mod, 3/4 turn pilot screw, DSP tapered header and pipe, IMS tank & YZ seat, Scotts dampener & triple clamp & Renthal Fatbar 971, White Bros suspension, Dunlop 756's.


i'm at sea level and pretty much everyone in the UK is-certainly england. i've got the same pipe as stefe9999 and it was for every country (including canada by the way) except the USA.

if you have read in the past "snap..." and "more snap..." as well as the latest "jetting Q's" you'll know how ALL my experiments were about keeping the needle as high as possible so as to keep the "snap" at low throttle.

now that you've got your APJ on such a short amount you are feeling the same symptoms as me.

it's a straight fact that the lower the needle in the ET the poorer the throttle response from standstill.

your first job is to make sure everything is OK at tickover (via the straight dimension) this with an 'N' i'm sure you have.

the other is to get the 4th gear/5th gear part right on the clip. this you have done.

so i'm afraid the 'snap' is the victim. "jetting Q's" was even trying to cure that very problem on saturday and yet again battle is joined.


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