Needle Differences

Motodude,

In regards to the Kehin needles: The OB tells you what the needle material is made out of and is inconsequential to this discussion.

The "D" in DVR denotes the taper of the needle in degree's.

The "V" in DVR denotes the L 1 length, which is the length from the top clip to the point on the needle where it is 2.515mm's in diameter. The shorter the L 1 is, the richer it is going to be with a given taper. And the longer the L 1 length is the leaner it is going to be for a given taper. Each letter designation in the L 1 length is 1/2 clip position different from each other, or .45mm different. (in the chart below you will notice that there is no letter I or O) So, the EKR that your 650 came with on clip position #2, would be equal to the DVR on clip position #7. This only applies to standard Kehin needles, I know for a fact that Honda needles are bit different when it comes to L 1 lengths and their letter designations. So, a DUR @ pos #5 is 1/2 clip position richer than a DVR @ pos #5 due to the DUR's .45mm shorter L 1 length.

The "R" in DVR denotes the straight diameter of the needle. This area of the needle is responsible for about 70% of mixture at start up and idle, with the throttle in the idle position.


http://www.keihin-us.com/needle.htm

excellent explanation !

Thanks whosa,

I have finally come to understand how this stuff works, I think. But, without Taffy's help I wouldn't have gotten here.

Dale

I don't know if it's in the doc or not, but, I know I have seen Taffy say that with the Kehin, you have to jet from the main on down. In other words, you've got to get the main right first, and then start working your way towards the pilot.

A change in the main of 10 or more will result in the necessity of changing the clip position. IE, if you go up 10 on the main (150 to 160) you will probably have to drop the needle a clip position, or in other words raise the clip on the needle and visa versa.

Recently I had started riding in the desert again after my summer riding at high elevation in the Sierra Nevada mountains at 8000+ feet and 80 degrees F. I was running a Honda NCVS needle up there, and when I came back down to 4000' and 60 to 70 degrees I was having quite a time getting it to start on the button. I tried putting in a bigger pilot, but was then too few turns out on the fms, less than3/4, and it still wouldn't start right. But, with the next smaller pilot I was too many turns out, above 2 & 1/2. When I would try to start it, it would crank over for a while and then start with a pop out the exhaust. If I turned the choke on it started right up, so I knew I was lean.

With that in mind, I realized that I needed more fuel at tickover, AND, I could split the difference between the pilots so to speak by going to the NCVR needle which has a thinner straight section, thus allowing more fuel. I went back to the smaller pilot and installed the R needle and wah lah! She starts up like a dream on the button and I'm right in the middle of the fms range at 1 & 3/4 turns out, and this gives me all the adjustment I need for changing weather conditions as sometimes it's bitterly cold in the desert or fairly warm.

Have a look at the Doc, Taffy has put a lot of great info in there about jetting. He has spent quite a bit of time and energy experimenting on jetting with both seat of the pants and dyno work.

the shoulder you are on about motodude (sorry, don't know your name) is well above the straight even. it's the equivelant of inside front cover of a 300 page book. before the print years, before the preface, before the bibliography, before the introduction.

the reason the needle works for all models is because they all have similar ports, carb and exhaust lengths and tracts. but most of all, even if they have different cams they have similar cams.

dale called me on friday afternoon (my time) and we had a chat. one thing he hasn't 'piddled' much with is the PAS. when he does this it'll all change again!

below are the rough ratios of PJ to PAS/PAJ.

35PJ needs 45PAJ or PAS
38 = 60
40 = 75
42 =90
45 = 100
48 = 100+ (who cares!)

too large a PAJ on a small PJ (for instance a 35PJ with 100PAJ) can lead to a flat spot just as you go onto the needle. i only ever discovered it on an "off to on" throttle when it just 'gasped'. you can whack up the PS to cover it but it then makes the bike too rich at or close to idle/tickover.

regards

Taffy

"Edit On"

Hey Taffy,

The above referenced PJ/PAJ numbers are exactly as in the doc.

"Edit Off"

Thanks for checking.

kzoo

to stop all confusion i went back and put it right. thanks for letting me know!. as i can't change your quote would you do summink wirrit fella?

thanks again.

regards

Taffy

Old thread new question!
I am looking for some advice on a needle, but will start with some background.
Start point
OBDVR C5
182 MJ
200MAJ
40PJ
100PAJ
1 1/2 turns PAS
Full A/P squirt.
Sea level 10 to 35 deg. C

First mod was new MJ 165, needle C6. Wow!! talk about a new bike.
Bit of a stumble going onto the needle. so A/P taken out of the equation.
The Bog came along. But the stumble was better, pretty much better everywhere but the snap.
Needle C7, better again everywhere. but the bog S*&#%ing me, PAS taken out to 3 turns, Bog much better starting no choke cold, and not starting warm.
PAS back to 2.5 and tiny little squirt from A/P. with small delay(about 3-4mm throttle opening).
Run out of clips on the needle and seem to be stuffing with the PJ setting the more i lift it, so here is the point. If I go to a shorter on the straight section should I increase the diameter of the straight to help lean of the low speed circuit?

first of all you mean that the PS is 3 turns out and not the PAS ok!

where is the bog? off a closed throttle in first or in third gear roll on?

you want to set the bike with no APJ at all. please turn this off completely. check your readings from the TPS as there have been problems with them.

regards

Taffy

The bog is off a closed throttle, not on the stand though!!! Thats a roger on the PS. love all the acronyms. The A/P was only put back on to enjoy riding it after I ran out of clip positions and jets.
TPs is as the manual states. And a new plug goes in before a session of testing.
I am confident about tuning the bike as every bit I of info I have dragged off this site has worked as expected. Its a real testiment to all of you devotees.A
ll my spares have to come by post, so am looking for some needles that people have had experience with, and feel are worth a try.

try the yamaha DMS needle. from yamaha. that should do it. or go for the EKQ for more top end.

if it was lean you would be able to gently open the throttle and have no bog right?

i would say that 160MJ and 38PJ should be bought whilst you are there.

regards

Taffy

You have just confirmed what I was hoping to hear, I got quotes today for 158, 160 & 162 MJ's. a 38 PJ and DMS, and EKQ needles.

I just needed a nudge in the right direction, before the credit card came out.

And yes it is possible to gently role through the lean spot without the APJ its just not much fun.

I have been looking at the HDJ emulsion tube, has anyone tried drilling some holes in the standard item?

Thanks

Tim

with smaller than 165 main try a 165 MAJ instead of a 200

your bike will love you for it at high rpm and make more peak tourque.

regards
Bushie

Cheers, Bushie

I have just bought a selection of twist drills to play with the Air jets. I have found when setting up mikuni/solex side drafts on cars that the air jets are critical for fine tuning when the rpm increases.

Tim