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Discussion Starter #1
Hi All

My current carb is dead, useless, hated.

So instead of crying myself to sleep trying to fix it every day, I'm replacing with a Mikuni 26 (given that the engine side mount of my current one has an inside diameter of 26.

Can I pick your collective brains on something?

1. Is 26 the right one? Should it be 28 with a new mounting flange to suit?
2. The jet sizes? I've googled around and seen people chatting about 22.5 for pilot and 170 for main, but not sure. (climate = Melbourne, Australia).

If anyone has any experience on this, please let me know - super keen to order and get this beast back up and running.
 

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Your figures sound a bit screwy to me - I'll have to confirm later as not near my PC until later

Couple of question in the meantime - is this the bike in your avatar ? - or is it a standard '89 ?
 

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Discussion Starter #3
Hey Purple, thanks for the reply.

It's the avatar.

I pulled the buggered carb apart (TK brand, seems to be stock) and it had a 40 pilot, a 100 main and a 2.75 needle - but the guys at Mikuni say those numbers won't relate to their carb; indeed, when I look around on google the numbers are more like what I said above (for that specific Mikuni VM26 carb).
Or did you mean numbers as in the 26mm vs 28mm?
 

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Working from memory (never a good idea), the carb should be 28 - main ranges from 126 to 130 (the higher number would probably suit your exhaust) - idle jet I'm not sure about. Those figures are for the TK, not the Mik, the Keihn might be different

Don't have access to the PDF manuals here at the moment - you can find them here https://www.tw200forum.com/forum/technical-write-ups/70-service-repair-manuals.html

Make sure you're looking at the slide carb, not the CV (the slide is the correct one for that year, and it's better than the CV anyway)

I'll come back later today with more details - until then, like I say it's from memory, so don't take it as gospel ....
 

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OK – back

Yes, the carb size is 28, although you could probably go up to a 33/34 if you really wanted to – recommendation is stick to 28

On these old style carbs, main jets start at 122, and go up to 130 depending on altitude. Recommend getting a few sizes in and tweaking it from there – with that exhaust on, you’ll “probably” end up at 126 (don’t quote me on that)

Idle jets depend on the carb manufacturer, most of them come “pre-loaded”, which is your starting point. One thing to be aware of, is that the thread pitch on some carb jets is different, so stick with brand. Do not go for some of the jet kits that are out there that say “126” etc. What is a 126 to them may be wildly different to a branded 126

If you want to go for “insane performance” (at a price), you can get a flat slide pumper carb - Mikuni-tm33-8012-slide-carburetor-TM33-8012

If you want a cheap Chinese knock off standard carb - https://www.tw200forum.com/forum/performance-customization/4977-carb-swap-comparison-3.html post#21

These cheap jobbies are becoming more common, but be aware that the throttle cables may feed from the opposite side, and require a bit of “tweaking” to get the cable sleeve to fit

If it was me – I’d stick to the standard carb, simply because I’d be able to get advice on how to adjust it jet wise – once you go “off plot”, we’re into the long grass real quick. If you do decide to go “off plot” a different boot size may be in order, but that’s a small detail

Your dollars, your choice …..
 

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Discussion Starter #6 (Edited)
Thanks again, Purple.

I hovered over the buy button on the VM28 for some time, but then went for the the VM26-606 with stock pilot of 22.5, a spare of 20 - 190 main with spares of 170,175, 180 and 185. (these are different, obviously but seemingly scaled accordingly to the stock).

There's good anecdotal evidence around of this carb suiting the bike, so I'm going to take a punt and hope it turns out okay. I think there's a human nature thing of thinking "VM28 or TM33... bigger numbers! faster!", but then it's only a 200cc bike....

I'll report back once it's fitted, tuned and running for anyone going through this in the future.

Thanks again for your input, much appreciated.

Oh, just FYI, I avoided the stock as I kind of resented Yamaha asking over $700 for it! I know there's 2nd hand, but you know... 2nd hand....
 

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I hope that works out, because I'm probably going to get a VM26 for my '87.
I'm not 100 percent decided yet if I'll go with the -606 version or the -8074, but I'm kinda leaning (no pun intended :D ) towards the former.
 

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Is that Web site saying they run a 21mm carb on the tw?
No, they recommend the 21mm on a TY175 (175cc).

The 26mm OKO K100 carb is recommended for the TW.

I had the OKO K100 carb that I experimented with a few years ago.,,took a lot of tinkering with... IMO, not worth the effort.

With the availability of a pretty good Chinese clone of the TK cv carb, not much reason to try others for a reliable carb solution.

That is...unless you are trying to get the the very last bit of performance out of the TW. :)

jb
 

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No, they're definitely saying 21mm for the TW200.

Yamaha TW 200
We have not had the opportunity to work on a TW 200 here, but have worked with owners of this Yamaha, replacing the stock carburetor, which no one seems to be happy with. After experimenting with a 24mm and a 21 mm, our clients chose the 21mm which gave excellent power and response throughout the throttle range. Owners we have dealt with have replaced the twin pull cable with a single pull cable. The carburetor fits directly into the stock manifold, but the airbox hose will need to be modified to fit. Once we have had one here at the shop to work on, we will provide the needed airbox adapter hosing with the kit. For now we offer the 21mm with the curved top, and jetted for the 200. We provide extra jets for fine tuning to your engine, exhaust, etc... and work with you to see you get it dialed in right. We believe this is the carburetor many TW 200 owners have been looking for to solve the woes of the stock carb.
 

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It ‘sez ‘ere

Owners we have dealt with have replaced the twin pull cable with a single pull cable
Simply because the 21mm they offer only works with the one cable

which no one seems to be happy with
Which basically means “we have no idea whether or not they’re happy”

Once we have had one here at the shop to work on
Meaning they have no experience of the TW

jetted for the 200
Jetted for a non descript 200

We believe this is the carburetor many TW 200 owners have been looking for to solve the woes of the stock carb.
“We believe” dances around the issue again — the next thing will be “up to 200% improvement in performance” — which means “if you only get 0%, we only said “up to”, no guarantee was offered or implied”

“In my opinion” - which I am by law entitled to - they’re full of crap — (two can play at that game) …..
 

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No, they're definitely saying 21mm for the TW200.
Thanks for the correction. Still not worth the aggravation of rigging and tuning it..IMO....but you are welcome to try.

A few years ago a TW owner tried the OKO carb and could only get it working by having the guys at MidAtlantic spend a considerable amount of time walking him through the set up.

I may still have the OKO carb (in NC) if anyone wants to try it....will need to wait until I return to NC next month to know for sure..

Also may have a VM26, along with 3 or 4 China slide carbs that were available before the TK clone became available.

jb
 

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Still not worth the aggravation of rigging and tuning it..IMO....but you are welcome to try.
Eh, maybe if they gave me a kit to evaluate, but I wouldn't spend money on it. I've been pondering swapping to another carb, but every time I get it in my head, I start thinking that cobbling together EFI for this thing would be fairly easy. There's a shop about 5min from here with a bike dyno, and doing back to back tests to see exactly what the gains are would be fun.
 

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Eh, maybe if they gave me a kit to evaluate, but I wouldn't spend money on it. I've been pondering swapping to another carb, but every time I get it in my head, I start thinking that cobbling together EFI for this thing would be fairly easy. There's a shop about 5min from here with a bike dyno, and doing back to back tests to see exactly what the gains are would be fun.
I’m kind of in the same boat. Every few weeks I want to try a pumper carb and see the difference. But then I think about effort and time versus results. Maybe at some point, idk. Kind of waiting to see if any other options or reviews pop up. We’ll see I guess.
 

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....... I've been pondering swapping to another carb, but every time I get it in my head, I start thinking that cobbling together EFI for this thing would be fairly easy.......
There's generic aftermarket fuel injection kit for single cylinder small displacement engines that has been mentioned before.



Don't know how "easy" it would be. I've thought the fuel injection system on the XT250 would be a good fit....but again, probably not all that easy or Yamaha would have done it.

For example, the XT250 service manual has about 25 pages just to explain all the "fault codes".....:eek:

jb
 

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I've seen the Ecotrons, but when I emailed them I was informed that they wouldn't sell just the hardware. I would want to add timing control to make full use of the added fueling capabilities, where their kit is just fueling.

Just on carb/EFI/fueling swap, I don't see much in the way of peak number gains happening, maybe 10% or so. I'm after more area under the curve. I'm not going to throw out things like "flat spots" and "throttle lag" as overall it's a smooth repeatable and reliable system when stock, but there is definitely some broadening of the powerband available by more accurately controlling fuel delivery. Throwing timing control into the mix would help get the full potential of this little motor to that chubby rear tire.
 

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I installed my VM26-606 today, and took it for a short ride. So far so good. I'll probably go for a longer ride in a bit.
 
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