Needle marking

P

Peejay

XS650 Member
Messages
29
Reaction score
0
Points
1
Location
Manchester, UK
I thought I posted this question but it seems lost somewhere so I try again.
During the carb rebuild on my 'stock 81/34mm model I noticed the marking on the rebuild kit needle was different to the original.
Not the square in square but the identifiers.

The original is marked 5HX12; the new one is marked 5Ix11.

Does anyone have a chart or the knowledge as to what the difference might mean.
I got the rebuild pack from Heiden based on the year and its marked as Made in Japan so I don't doubt it's a genuine item.
I used to work with SU carbs and know that a needle form can significantly affect performance & economy so I don't want to go ahead with the 'wrong' needle & have to waste time trying to set it all up again if it's completely wrong.
I have looked thru the Tech stuff and can't find a similar thread about these markings but may have missed it somewhere.
Any help appreciated.
thanks
PJ
 
The 5IX11 came on Canadian models, and is richer than the 5HX12 which came on U.S. models.
If you have both, than I'd try both. You can remove the tank and swap needles without removing the carbs.
 
Thanks DogBunny,
I read or maybe misread the guide at amckayltd.com/carbguide and was not sure whether the reference:
'The 5 series needles in the later carbs, on the other hand, have 2 very
different tapers to them. You should notice a difference in the way the bike runs by
swapping them' as being different to 4 series needle rather than to each other.
Also it talks more about these needles in 38mm carbs I think.
The chart in the guide does not show 5IX11 as being suitable for 34mm carbs.
It sounds as if the richer Canadian spec was not as critical on emissions at the low/mid range which I guess can be handled via the mixture screw
I am not worried about the high end being rich.
Would that be a fair assessment?
I am going to start off with the 5IX11 as the originals were pretty worn on one side and have estimated that the 2nd notch from the top puts the taper start on the new needle about equal to the old needle position, does that sound reasonable?
I'd still like to see a chart of the needle dimensions along the length if anybody has one because I used to machine prototype SU carb needles and then tune them for performance, just geeky I guess!!
Thanks again
PJ
 
It's confusing, I'm not sure what the carb guide is saying. Maybe 5twins will chime in since he co-wrote the guide and the chart.

The chart only applies to US models.

The leaner needle on the US models was to comply with the new EPA regulations of the time. Canada did not have these regs, and could use a better-running, richer needle. I would try both needles. What really matters is what mods you have made, if any, and what re-jetting you do. Also, note that you can adjust the height of the Canadian needle.
 
I am pretty cool now with your explanations DB, I just did not want to install a new needle and end up chasing the impossible dream!
The mods are straightforward so far, Ramair fitlers, straight thru 45mm headers & tail pipes.
I got the pilot jet & main jet sorted with those & then didn't want to step into the abyss of a needle that was a million miles away with no hope of getting home.
It may run richer now but I can twiddle the jets & mixture to get home now.
I do not like worn needles as the 'oval' effect changes atomisation of fuel giving inconsistent mixture at a given throttle opening, geeky huh!
I'm going forward and that's great, thanks again.
PJ
 
If your needle is oval shaped it must have been hitting the needle jet. Kinda makes me think a new needle isn't going to solve the problem without a new needle jet as well.

Canadian Needle jets have more holes on them compared to the US needle jets
 
The 5 series needles I was referring to in the carb guide were the 5O2 needles in the '78-'79 BS38s and the 5HX12 needles in the BS34s. If you're going to attempt any needle swapping, it helps to understand a little bit about how Mikuni labels their needles. They come in different series that span 10mm length ranges, and the first number in their code denotes that. A 4 series needle falls somewhere between 40 and 50mm long, a 5 series would be between 50 and 60mm long, etc. Now, the clip slots on a needle change its height by 1mm, and as you're probably aware, changing the needle clip position by one or two slots can have a very pronounced effect on how the bike runs. So, just think what substituting a 4 series needle that is, say 5mm shorter (or maybe even more) than the current 5 series you're using is going to do. Plain and simple, it just won't work.

The letter or letters after the first number indicate the angle of the taper or tapers. Supposedly, one letter has a single taper, two would be a double taper. I have no idea what angles the letters denote. I guess that's one of Mikuni's little secrets, lol.

The last number is what Mikuni calls a "factory reference number" and once again, I have no idea what that means, lol.

Now back to what I was discussing in the carb guide. If you compare the 5O2 from the 38s to the 5HX12 from the 34s, you'll notice the tapers and, in particular, the points are quite different. The 5HX12 has a much sharper point than the 5O2. That's why I said you would notice a difference if you swapped the two. I really don't see the point in swapping the "fixed" 5HX12 into a set of '78-'79 BS38s. You'd lose your midrange tuning capability. The 5O2 could be tried in the 34s though. Even though the tip is fatter, the rest of the taper is narrower so should make for a richer running needle overall. The length is the same as the Canadian needle, 50mm from the top clip slot to the tip.

What would be desired for the '78-'79 BS38s is an adjustable needle with a sharper point, and I just happened to stumble across one, the 5Z1 needle used in the '77-'79 XS400 carbs. It measures the same from the top clip slot to the tip (50mm). It is fatter (leaner) through its middle section so would probably not be a good idea in a totally stock machine. If you've modded and re-jetted though, you usually need to lean your midrange anyway. Here's a pic of the three needles compared .....

Needles.jpg


I've tried the 5Z1 in my '78-'79 BS38s and it made a nice difference. The bike was snappier off the line and seemed to pull harder and rev quicker through the low to mid RPMs. I've never tried them in the BS34s but I think they'll work for them too.
 
Last edited:
That's the whole problem I'm having. Overlap in my 34s. Need my 140mj need my 45 pilots. I had it ironed out better by shaving the plastic donuts to drop the needles. Still cuts out (not near as bad)around the 3 to 3500 rpm hard throttle. So I'm trying the cdn needles and jet.

Question. Last go round. I dropped the fixed needles in my bs34 one more last time by taking more plastic from the donuts.. It did fix the cut out but I had a lean surge cruising around at low throttle openings. Is this where I would step to a 47.5 pilot? Getting close. But old man winter got in the way.
 
XS John used to like his homemade "46" pilot. He reamed out a 45 with a guitar string or something. You can achieve pretty much the same thing by reducing the air jets a little. The air jets are small round mains like used in the BS38s. The stock size is a 135. You might try a 132.5 or a 130. This will put you somewhere in between a 45 and 47.5 pilot. You may even have them on hand from tuning your '74. They're about the easiest jet to change because they're in the edge of the intake bell where the pod filter clamps on.
 
That's a good idea on the air jets. Always over look those. These 34s are on my 74.

I have a nice set of xs400 needles....in my running 400. Xs400 carb parts seem a lot more scarce on ebay. Also have a set of the 502 needles from a set of late 38s.
 
They do pop up occasionally. In fact, I just scored some 5Z1 needles and XS400 carb tops off eBay a few weeks ago, $8 for the needles, $12 for the tops. Why carb tops you ask? Because they're alloy and will swap right on the BS34s to replace those often rusty and ratty looking tin tops .....

34 Alloy Tops.jpg


34 Alloy Tops2.jpg


SpareBS34s3.jpg
 
Last edited:
So an update,
I fitted the 5Ix11 needles using the second groove from the top from the clip because that aligned the start of the taper with the previous needle. It may be that the needle is richer as advised so a lower needle start point may not hurt?
One thing I noticed is that the new needle groove created a 'sticking point' for the plastic bias washer and prevented the needle sitting tight on top effectively raising the needle about 1/2 a groove or more so I made sure that the clip was firmly 'gripped' that is it would not rotate before final install.
finally I decided to order 2 diaphragms from JBM after reading good things and, fantatstic !!! >$20 each + postage came to about £40 and delivery was well fast. no import duties so a great deal & a great service from Don James.
Thanks for all the help
PJ
 

Similar threads

modieselguy
1974 TX650a Carburetor Question
Replies
9
Views
287
5twins
5twins
Nicko
Gearbox blues
Replies
5
Views
365
Jan_P
J
ebbaga
XS650F misfire between 4000 and 5000 RPM. Boyer ignition.
Replies
3
Views
376
Raymond
Raymond
E
Carburetors from hell
Replies
1
Views
226
jpdevol
jpdevol
H
has compression, spark, and fuel but won't fire / start - cam chain issue?
2
Replies
36
Views
1K
Jan_P
J
Back
Top