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If the air passages are completely clear, then you may want to replace the idle jet and maybe the mixture screw.
First the idle jet, then mixture screw...but if ordering parts, you may want to order both.
 
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Discussion Starter · #23 ·
I have done more tests today:

I disconnected the choke and throttle cables and tried to regulate the idle and got it with the mixture screw loosened two turns and the idle screw 5 and 1/2 (the latter seems excessive to me, it would be interesting to know with how many turns they left the factory, in other carburetors it is about 1 and 1/2). With this configuration both screws act as they should on the engine and the mixture was correct after checking the spark plug.

At this point I went to check how it behaved when accelerating and there the mixture was enriched (some black smoke from the exhaust and spark plug with soot), decided to change the needle clip one position higher (2nd from the top) and this returned to uncontrol the mixture at idle and the screws stopped responding again. Something is not right.

@SportsterDoc, yes I cleaned every duct in the carburetor and made especially sure the small holes at the bottom of the air intake were clean.

As you say I thought about looking for a rebuild kit for the carburetor but I see that it's not going to be easy to get (at a reasonable price), possibly those for other carburetors will do but there is also no information from the manufacturer (Teikei) with detailed information that would allow me to compare dimensions and so on.
 

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I have done more tests today:

I disconnected the choke and throttle cables and tried to regulate the idle and got it with the mixture screw loosened two turns...
Perhaps the throttle cable was opening at idle, instead of cable slack?
 
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Discussion Starter · #26 ·
Exactly, that's what I thought since it explained the problem because if so the slide would not lower enough for the idle speed screw to have an effect and this would also explain that the mixture screw would not work because if it is not completely lowered the idle speed circuit does not work or only partially and the others come into play. So I disconnected the cable and also saw that it was not in the best conditions and after making the adjustments and seeing that it started to work I thought I found the problem, but when accelerating.... (what I said before)
 

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Discussion Starter · #27 ·
The fact that the adjustment was achieved with the idle screw loosened more than 5 turns is what makes me suspicious, because if this were really approximately the correct value (from the factory) it would imply that the problem is most likely in the main circuit ( in the needle or the jet) and not in the mixture screw or the low circuit
 

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Discussion Starter · #28 · (Edited)
I am in search of a rebuild kit for the carburetor. I've been doing some research and the conclusions I've drawn so far are:

- Original parts: in the stores I have consulted the price of the set of brass parts is almost half the price of the carburetor... so it is not cost effective.

-KEYSTER: it does not have a specific kit for the TW 125 as far as I have seen, but there are kits of other models that share carburetor that have parts in common, that is to say they have all the parts that I look for but distributed by several kits.
I have read reviews on this forum not very good about this manufacturer, but the dissatisfaction seemed to me more for the fact that they were not the right size parts than for their quality.

-Tourmax CAB-DY13: this kit is intended for the TW 125, but I have not found a description of the needle and jets sizes. From the picture some components do not correspond to those of my carburetor.

-All balls: I see that they also manufacture a rebuild kit but not for the TW 125.

Does anyone know of any other kit/manufacturer, or know where they can be obtained?

In Japan it should be relatively easy to find them, but it is difficult to search because of the language.
 

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Discussion Starter · #29 ·
Someone here knows how to know the measurements of a Teikei jet needle from its code, the one I have mounted is 4C78-3/5 and I would like to know the differences with respect to a 4C9A sold by Keyster, but I can't find information for Teikei coding (there is for Dellorto, Keihin, Mikuni).I consulted Keyster but it seems that customer service is not their strong point.

*Mental note: never buy a bike with Teikei parts on it again, especially if it's a Yamaha.😂
 

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Here is a start

See also page 28 of the service manual PDF

 
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Discussion Starter · #31 ·
Thanks, I already checked it out it was a very similar case to mine and I also discussed it with Tris, really the only kit that may work is:

Product Rectangle Font Material property Parallel



But the jet needle is different and no idea how much is the difference.
 

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Discussion Starter · #33 ·
Might be difficult getting dimensions, even for Mikuni

Keihin is easy. Numbers are mm
Example: 44 pilot is .44 mm
165 main is 1.65 mm
In the jets there is no problem because they match (without knowing what the number indicates). But the needle has some codes that I do not know, for Mikuni and Keihin you can find tables and graphs with the sizes but for Teikei not even looking on the web and forums in Japan.
 

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Sorry to not be of help.
Be good to find a chart like this Keihin (courtesy Nightrider.com)
The 27094-88 is the famous N65C needle used in 1988 Sportsters, which did not have an accelerator pump, thus a rich needle. It should have been at the top of the needle chart.
Font Pattern Parallel Rectangle Symmetry
 
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Discussion Starter · #35 ·
The solution will be trial and error, I will order it and see what arrives🤞, I do not have much confidence according to some comments and it seems that they do not respond to mail as in the case of Tris, but well the alternatives are few.
 

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Discussion Starter · #36 ·
I also add the post in case it is useful in the future for someone, that in addition to the companies mentioned above in the USA is 6sigmaracing that makes kits for the TW125, but I think only a few components.
Dynojet also makes kits but you would have to check if they have the necessary ones.
 

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The problem with Dynojet, at least for the Keihin CV40, is that the emulsion tube (main jet and needle jet holder) is a different thread size than stock. Without changing the emulsion tube, rejetting the main on a Dynojet kit requires using Dynojet main jets.

Stock Keihin is 6mm
Dynojet is 5 mm

Very irritating when a turner has a bin of stock jets and cannot use them!
 
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