New to me XS 650...

I'm not a 38 expert but I believe the needle jet comes out the bottom... float side. You'll need to push from the top, so yeah the slide needs to be out of the way.
Maybe one of our resident 38 experts will chime in here.
Just out of curiosity, why are you removing the needle jet?
 
The BS38s are a rather odd carb. The main and pilot jets mount into the float bowl, not into the bottom of the main carb body like on most other carbs. You access the main through the drain bolt hole. This makes quick main jet changes with the carbs still on the bike pretty easy .....

sDP6nOS.jpg


The emulsion tube and needle jet are combined as one, and it is just a snug push-in fit into the bottom of the carb body, not threaded in. Here you can see the needle jet with the needle sitting in the center of it. You may not need to remove the slide to get it out, depending how tight it's in there .....

U4v6TJu.jpg


Here's some needle jets removed, showing the o-ring that seals them. Only 3 different sizes were used in the 38s and other sizes weren't commonly available so it's rare to find them changed .....

cyGGqbT.jpg


The '76-'77 carb set had the Z-8 stock, the largest (richest) size used.
 
I didn't realized they sat that far down in the bowl. Long as they're not stuck from gunk and age they twist out pretty easy 5twins?
 
Jim said:
I'm not a 38 expert but I believe the needle jet comes out the bottom... float side. You'll need to push from the top, so yeah the slide needs to be out of the way.
Maybe one of our resident 38 experts will chime in here.
Just out of curiosity, why are you removing the needle jet?
Click to expand...
Thank you for your consideration. I am working through a "New to me" XS650. It has been 750 kitted and except for new ignition, I do not know any other mods. It is running rich. I dropped the Needle 2 notches which has helped. But around town I am still "burbling" under light load. A plug reading after 45 + mph riding is light chocolate on the insulator. Black after around town riding. So.... I want to get an idea of where my carbs are at so I can plan on what steps to take and what jets I may need. I appreciate all the positive input. I try to scan other threads or the Technical Resources post for info before I ask a question so that I am not asking a question many of you old hands answered yesterday or last week.
 
Jet needle looks to be awfully worn. If the needle is so would the needle Jet be.........

That has to have quite an effect on the jetting sizes

Remember XSjohn's needles, when he was doing his initial work on the needles. He sanded the thin coating off the Jet needle to enrichen, then made his main jet a half size bigger, (with a guitar string), to compensate..........
 
Well yes, the needle jets stick pretty far down into the bowl, but not into anything. They are only a tight or snug fit on top where they fit up into the carb body, that is, if the o-ring is good. When I got my '78, the needle jets were so loose in the carb body, they would fall right out. Their o-rings were really shot, all shrunk up. New o-rings restored their proper snug fit.
 
5twins said:
Well yes, the needle jets stick pretty far down into the bowl, but not into anything. They are only a tight or snug fit on top where they fit up into the carb body, that is, if the o-ring is good. When I got my '78, the needle jets were so loose in the carb body, they would fall right out. Their o-rings were really shot, all shrunk up. New o-rings restored their proper snug fit.
Click to expand...
My take is that I can remove the drain plug and determine the main jet #. I can compare that to the chart. It was mentioned that 122.5 is the original size. That seems easy enough that I could do that in 10 free minutes, so I will give myself an hour. :)
 
gggGary said:
Those needle jets often glued in with varnish. Use a heat gun to loosen them.
Click to expand...
I will just remove the main jet because this is a binary question. If the main is the correct 122.5, I have a bigger problem. If the mainjet is 2 or 3 sizes over original the solution would seem to be straight forward, order a couple of pairs of smaller jets.
 
As I mentioned earlier, your '76-'77 carb set would most likely need 3 or 4 sizes larger for your mods. But, if the P.O. read jetting recommendations on the web, he may very well have put something in the 140 range in there. About the most your carb set will take with the large Z-8 needle jets is something in the mid 130s. I tried out a set of '76-'77 carbs on my bike. I have similar mods (pipes and pods) and the biggest main I was able to run was a 132.5.
 
Yes, that may be a bit too large if you still have the stock Z-8 needle jets, which you probably do. As I mentioned, needle jets rarely got changed. I'd get some 135s and 132.5s to try. When your jetting is close, sometimes one size change makes all the difference in the world. In your case, it will probably really help cleaning up those black plugs.

Just let me say that it's very easy to over-jet these CV carbs because they work on engine demand. The slide only opens as much as the engine can use. Just because you whack the throttle wide open, that doesn't mean the slides are going to go wide open. That's why they will run somewhat OK with jets that are too big.
 
5twins said:
Yes, that may be a bit too large if you still have the stock Z-8 needle jets, which you probably do. As I mentioned, needle jets rarely got changed. I'd get some 135s and 132.5s to try. When your jetting is close, sometimes one size change makes all the difference in the world. In your case, it will probably really help cleaning up those black plugs.

Just let me say that it's very easy to over-jet these CV carbs because they work on engine demand. The slide only opens as much as the engine can use. Just because you whack the throttle wide open, that doesn't mean the slides are going to go wide open. That's why they will run somewhat OK with jets that are too big.
Click to expand...
Thanks 5twins, I was tending to 132.5. Where do I order them. Mikesxs seem cumbersome and the mikuni website is too. I have been searching for an hour!
 
Many get them from Niche Cycle. Make sure you get genuine Mikuni jets. You need what is called the small round main, actual number is an N102.221 .....

iqgtOaY.jpg
 
Yes, you can identify genuine Mikuni jets and needles by looking for the trademark "square in square" emblem stamped on them .....

5Pb9lAT.jpg


You can see it on the jet head pictured above as well, just to the right of the "R".
 
I should also mention that the K&N pleated type pods aren't the best choice for these CV carbs, they don't work that well. The pleats can disrupt the air flow, make it "rough", and that can mess with the slide lift. For pods, the best choice is the straight foam UNIs .....

1GjnNlo.jpg


These carbs also don't like a tapered filter, which most K&N style are, but I see yours are the straight type. They may work a bit better but if you still have tuning issues after down-sizing the mains, I would change the pods.
 
That is next on the list. I saw that "pleated filter" issue in another thread. In the meantime, while removing these jets is easy, how do you flip the bike over to reinstall them? On the same note, does anyone need ONE 137.5?
 

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