72 XS2 carb rebuild help

I don't know about the taper, but the needles that went in were, for sure, the same length as the Y22s that came out.

Matt
 
That may be so, they could be the same length. That might mean the ones you pulled out are Y22's too.
You did say the PO rebuilt the carbs, he may have put the wrong needles in.
Leo
 
Yes, the needles, not the jetting are probably the problem. It's likely that someone before you put a re-build kit in that also had those incorrect Y22 needles, and they tossed the proper ones. PM me if you need the 4JN9 needles, I have a pair I can sell you.
 
I'm having the same problem on a 72, it runs really well but black carbon plugs in a hurry! How do I tell the needles r they stamped with the number!? I'm going to be tearing them apart here to investigate!
 
I got my new needles in (Thanks for the offer, DogBunny. I had ordered before I saw your post). The don't say 4JN19, but some rectangular symbol followed by JN19. I read somewhere that 4 means the retainer goes in the 4th slot.
The ones I got from MikesXS are exactly the same length as the Y22s that came out and if the taper is different, it's in a couple of thousandths. They seem identical.
So, they're the wrong ones, too, I assume?
XSLeo indicated the Y22 are too short.

Thanks,
Matt
 
I don't know if the needles that you got from MikesXS will work or not. A couple years ago I got a chance to look at a MikesXS so-called 4JN19 needle, and it was clearly a counterfeit, with a very crude fake Mikuni square-within-a-square symbol stamped into it, a very crude 4JN19 stamped into it, and the package that it came in said "Made in China." The clip slots were wrong too, they were too wide, which allowed for slop. I suspect that this is what you got. Real Mikuni parts are made in Japan. Real 4JN19 needles have not been available new from Mikuni for a long time.

The 4 in 4JN19 does not refer to the clip slot. Clip slot comes after a dash after the needle number, for example 4JN19-4 refers to a 4JN19 needle with the clip on the 4th slot from the top.
 
Yep. The "square within a square" is the symbol.
So, where do you get the real thing if they're not available?

Matt
 
I still have a good used pair that I can sell you. There are also NOS ones on eBay if you know how to find them. But since you already have them, first you should try the fake ones that you bought and see what happens.
 
I have to have my bike running by next Thursday night. My son and I are heading for Vintage MC Days in Ohio Friday morning early.
So, if you'd be willing to send me your needles and trust me to send you payment at the same time, I'd appreciate it.

PM sent

Matt
 
The conclusion...so far...
After the above post, DogBunny had me call him and after some discussion, we decided that my needles were identical to the original ones he had. I sent him a picture of my carb to make sure I had identified it correctly. I had.
I had changed the jets, but there was no difference, even running with the air cleaners off. So, I put the stock jets back in.
DB said he really didn't have any more ideas. I had cleaned, rejetted, replaced the o rings...wait...what o rings, I said.
So, he sent me a set of the little o rings that go around the emulsion tube.
I finally got around to installing them and it seems like everything is fine now. Starts easy, idle is good, plugs are not sooty.
Unbelievable. Probably been the whole problem since I got the bike three years ago.

Thanks for all the help,
Matt
 
The Y22 generic needle may work in the '70-'73 carb sets as it is the same length (40mm from top clip slot to tip) as the 4JN19. I'm not sure how the taper matches up though. The problem is, many of the rebuild kits for later carb sets contain this needle and it's way too short for them. They need a needle about 5mm longer. This is due to the change in design of the main bore. '70-'73 carbs had a raised floor in the main bore. This required a longer needle jet and a shorter needle .....

EarlyRaisedFloor.jpg


On later BS38s, the floor was dropped, and this required just the opposite - a shorter needle jet and longer needle .....

LateCarbThroat.jpg
 
Or so I thought.
My son and I have been on a couple of rides totaling close to 200 miles. He said it smelled like I am running rich, so I pulled the plugs and it still is.
So, as a last resort before I replace the carbs, is there any reason I shouldn't move the clip in the needle from the 4 slot to the 3 slot (that would lean it out, right)? Almost all of my riding has been in the 3500 - 4000 rpm area, which is in the mid range, isn't it? And doesn't the needle jet govern the mid range? It's the only thing that's really adjustable outside of changing jets, which I tried.
Here's my reasoning for thinking it could be this- - I replaced the diaphrams with JBMs and the clip slots are a little sloppy on my counterfeit needles. Could that not create enough difference to necessitate a slot change?
Are there any brand new carbs available that would fit using my stock air boxes?

Thanks,
Matt
 
Hey, Matt. Interesting situation there. Of all the oddball, out-of-the-box, PO abuse, disintegration scenarios, the only one I can think of that would cause an over-rich condition in BOTH carbs simultaneously would be in the XS2's shared enrichner system. A bad/rotted starter plunger tip (or plunger seat) *could* weep fuel into the starter circuit. My carb rebuild album focuses on the unusual stuff, and has a pic of my old/rotted starter plunger tips. Of course, you have to view the album backwards, last-to-first.

http://www.xs650.com/media/albums/2684/
 
I guess I thought the enricher -that's the "choke", right - only operated on one carb. There's no linkage to the other carb. How does fuel get across? Through one of the two tubes and that run between them?

Matt
 

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