All you need to know about needles
Posted September 07, 2001 - 11:21 PM
ok, well i'll explain some of it. you print this off and then go read it once, read it twice and then read it again until you've got the whole picture.
the needle has three letters. let's say its an ELN needle for example.
the first letter, 'E' denotes how sharply the needle tapers to a point. the 'D' needles are 3/4 of one degree and the 'E' is 1 degree.
what does it mean? (cause)
well the thinner the needle gets toward the tip means the more fuel can get between the tube and the needle. so it will run richer.
what will happen? (effect)
if your bike needs that extra fuel it will go like snot, in the WR's case this is what happens. not the needle if you ever want totally placid control (ie pleasant trails)
i'll skip the middle letter and do that last. let's go to the third letter.
_ _ N
this letter is the straight bit. simple. as the letters go up so does the size of the needle. so an EKN is slightly thinner than an EKP for instance.
what does it mean? (cause)
a thinner needle will run slightly richer at tickover and in that area where you open the throttle from closed.
what will happen? (effect)
you may have a slight hesitancy and need a thinner needle. does your bike stall a lot?now remember it is just tickover and about the first 2 yards that you ride ok?
in my experience the _ _ M needle was the sweetest my bike ran at tickover. they're thin needles. i've got the EKP and it's what was recommended and i'm happy. just recently Yamaha have gone to _ _ N needles which is in between.
and now the one that ****s us all up! the middle letter! _ L _
all needles are the same length so to make a needle taper thinner with the same taper, you have to start higher and higher up the needle.
life would be easy if we only had one straight diameter and all the needles just got machined to a narrower and narrower point. we could all **** off down the pub and live happily ever after.
unfortunately with the needle thicknesses going in and out, the angle of taper changing and all, we can't get a baseline of how thick a needle will be say at 1/2 throttle. there would be no measurements.
so to get over this keihin have a measurement, 2.515mm. and they measure from the top clip position every time to wherever the needle is 2.515mm width as the needle tapers in. whatever needle shape or size. 2.515mm ok?
so if i have an EKP needle and you have an EVP needle my needle has the same width and angle of taper as yours but my _ K _ needle is thinner everywhere than your _ V _ needle along it's taper. that means also that it will be thinner at the tip and that the taper will have started higher up on my needle.
so how do we compare an EKP and an EVP needle?
well both needles are 2.515mm at some point aren't they! the wider taper needle (EVP)will be 2.515 lower down and an EBP (for instance) will be 2.515mm very high up.
Keihin therefore give a letter to each point that a needle crosses this line.
an EBP is therefore crossing that line very early and a EVP very late!
every second letter is worth one clip position so that an ELN is the same as an ENN
as long as i lift the ENN needle one clip.
here are three straight examples
eJn on clip 3
eLn on clip 4
eNn on clip 5
are all the same. if you have an eKn or an eMn you are simply operating between clip heights to the ones named above.
remember low letter = richer needle (thinner)
if you now try and put this in order in your mind it goes like this;
distance down to the middle letter, now the taper angle (E _ _) which when drawing the two sides of the needle will draw the lines in or out.
finally the width of the needle. that middle letter is your anchor point from which you decide which needle you need.
the needle effects mainly mid throttle and is most noticeable for the average bloke accelerating; in 2nd and 3rd gear.
hope this helps folks!
Posted September 08, 2001 - 06:48 AM
Great job for the explanation! Thanks for taking the time. I was just about to ask about this. My new 01WR426 has the Kehin FCR39MX on it and it has a needle that is a little different from most I see people talking about. According to my manual, I have the OBDQR needle. I assume the trailing 3 letters are the three you speak of. Don't know about the OB. Given that mine is a DQR, here's a couple questions
1. Most seem to have the E
2. Most also seem to have letters more like n,j,p for the ending letter, so they're thinner than mine.
According to your analysis, I have a fat needle with a short tapered section. My bike does have the misfire/rough running problem around 1/8 to 1/4 throttle (just like northernryder was having). But when you give it full throttle, it just rips. To try to fix the roughness, I have raised the needle from the 4 position to 3. Did this based on other posts I've read. but have not ridden it yet.
Any thoughts on the needle I'm using?
Posted September 08, 2001 - 09:47 PM
yes it is the last three letters. also the last letter is normally an M, N or P but never a J!
yep you have a needle that barely has any angle (D _ _) and the taper is low on the needle in that it's the letter Q (_ Q _ ) and lastly the straight bit is fatter than most. (_ _ R)
your problem is in the same area as mine. but mine is HEAVILY modified so that it could be one of half a dozen different things.
i'm not going to even start to try and take over from JD. i'm quite good at diagnosing rich from lean but i don't compile lists of formulae like JD.
it's not for me.
the area you are concerned with is pilot jet and pilot screw. it's also where the needle starts to work.
air reacts quicker than fuel so when you say that opening the throttle helps it means that it is rich and that the more you snapped the throttle means you nearly made it the correct ratio. therefore you should try leaning the mixture by turning the pilot screw in.
i don't think that it's a needle problem but if it is you should drop the needle one.
JD and i still talk differently on some subjects and he does have a lovely idle while i have a very good tickover!
one thing i would encourage anyone to do is NEVER talk about moving the clip (cause) but talk about lifting or dropping the needle(effect). if you're running rich you should have DROPPED the needle from clip 4 to clip 3, ok?
as for you kev, how the B***** hell did you find out my name?
Taffy (David Lloyd)
Posted September 08, 2001 - 11:08 AM
David, I e-mailed you at home awhile back on my carb. When I received your reply, I was thinking, "Who the hell is this".
[I tried to highlight your quote in my response, but have not figured it out...]
[This message has been edited by NH Kevin (edited September 08, 2001).]
Posted September 08, 2001 - 04:47 PM
To add to this: The first 2 letters will give a close idea of where the taper starts. This is a critical area that is altered by changing the clip.
One of the first notes I put in my personal jetting information was that DV- and EM- needles have their tapers start at nearly the same place on the needle. These were measured and compared at 2.70mm.
The result is that both DVP and EMP are commonly used in clip #5 (which is EKP in #4).
DTM is commonly used in clip #3 (DXM#5) which would be similar at tickover to EKM#3(EMM#4). Something for Taffy to think about.
Posted September 08, 2001 - 05:19 PM
Also, what is the tickover point? In my jetting studies, I think you mean the throttle position where the jet needle's primary effects start, about 1/8 throttle.
Posted September 08, 2001 - 07:30 PM
Posted September 08, 2001 - 10:38 PM
Posted September 09, 2001 - 01:01 AM
tickover in britian, is idle in the states.
Posted September 09, 2001 - 04:58 AM
I think I am the first to say my bike runs best on DVP#6 which I didn't want to try. Everything else stays the same.
3/4 fuel screw
Posted September 09, 2001 - 12:46 PM
I now have the stock US exhaust with the plug removed. I bet the DQR that I have is for the restrictive European pipe that came with the bike. BTW, so far I'm WR timed.
I rode it today, and it still has the same problem, but I can describe it better now. The problem is rough running, like its missing. It happens at about the mid-rpm range when I try to keep the speed constant. The problem is not at low RPM like I had thought. Only change so far is I dropped the needle from 4 to 3. Also when I let off from high speed, I will get a large backfire. My needle position matches your Jetting prediction chart pretty well. I'm call my riding 6,000 feet @70c. Your chart would call out a ~#153 main (have #158). Any thoughts on this problem? It is a fairly narrow RPM range that has the problem, but it sputters pretty bad when its there.