75' RD125B Rebuild - Suggestions

[Sleeper217]

I'm still working on my 75' RD125B resto-mod and have come to the conclusion that I need to go with aftermarket carbs.  I'm leaning towards Mikuni VM22's.  However, I would love to hear from anyone who has switched from stock carbs to aftermarket ones.  What say you fellow 2T fans?

Best regards

[JKV45]

I'm still working on my 75' RD125B resto-mod and have come to the conclusion that I need to go with aftermarket carbs.  I'm leaning towards Mikuni VM22's.  However, I would love to hear from anyone who has switched from stock carbs to aftermarket ones.  What say you fellow 2T fans?

Best regards

Curious how you reached that conclusion.

[sav0r (CL MotoTech)]

If they are like my TeiKei's they are probably rotting off. Hard to find replacements in nice condition.

I did DT125 inlets and reeds with knockoff Mikunis. I rode the bike for a summer but fought other gremlins the entire time. The knockoff Mikuni's ran fine. It was surprising. I had to get a throttle cable to make it all work.

[Sleeper217]

Curious how you reached that conclusion.


Thank you for responding to my post.

My conclusion, more like an acceptance, stems from the fact that the original carbs I have are in disastrous shape and parts are hard to find.  In addition, for my purposes and intentions for the bike it would be more economical and practical to go with aftermarket carbs.

[Sleeper217]

If they are like my TeiKei's they are probably rotting off. Hard to find replacements in nice condition.

I did DT125 inlets and reeds with knockoff Mikunis. I rode the bike for a summer but fought other gremlins the entire time. The knockoff Mikuni's ran fine. It was surprising. I had to get a throttle cable to make it all work.

Thank you for the feedback.  My carbs are in similar condition.  If you don't mind sharing, what size carbs did you go with?

Regards,

[JKV45]

Curious how you reached that conclusion.


Thank you for responding to my post.

My conclusion, more like an acceptance, stems from the fact that the original carbs I have are in disastrous shape and parts are hard to find.  In addition, for my purposes and intentions for the bike it would be more economical and practical to go with aftermarket carbs.

I would talk to Gordon from Custom Carb Service (https://www.customcarbservice.com/) before buying new carbs.

You could send some photos and specs, and see what he says.  I've known him for quite a while, and he is a straight-shooter and very detailed.  He will let you know if they are not usable or repairable.

Gordon is well known for saving plenty of really bad Ninja 250 (among many other) carbs. The photos on his main page show some good examples of before and after.  There are some really bad before pics.

[SoCal250]

The OEM TeiKei carbs on the RD125 are crap. Poor design, hard to get parts (jets, etc.). Yamaha only used the TKs on the  RD125 & RD200. If yours are damaged or missing parts there's no sense in trying to resurrect them especially if the bike isn't all stock. The only reason I'm still running them on my RD125 is that it's 100% original and a multiple show winner, otherwise I'd upgrade to Mikunis in a heartbeat.

Because the TeiKeis have an integrated angled flange anything you upgrade to will need new flanges to adapt them so the new carbs sit level. You can use Yamaha OE manifolds from a CT2 or DT125A and then bolt up flange-mount Mikunis, like VM20-273. No difficult mods involved, just have a custom lower throttle cable made.

I wouldn't go too large on the carbs especially if you're not building a hotrod engine or you may run into performance issues. If the throats are too large you end up losing velocity causing atomization problems with the fuel charge. Since the OE carbs are 18mm I'd try to keep it at 20mm, which is the size used on the 200. One of my many projects down the road is to get my second RD125 going and the tentative plan for that one is VM20 Mikunis on DT125 manifolds (already have the manifolds in my stash).

[Guygrrr]

https://www.treatland.tv/yamaha-DT-MX-mikuni-VM-intake-p/yamaha-dt-mx-intake-bolt-on.htm

I'm sure there are other places to get them, but this is the DT manifold in question.

[SoCal250]

https://www.treatland.tv/yamaha-DT-MX-mikuni-VM-intake-p/yamaha-dt-mx-intake-bolt-on.htm

I'm sure there are other places to get them, but this is the DT manifold in question.

Personally I would track down some used OE Yamaha ones. Reading the one review on that part from Treatland is reason enough.

[sav0r (CL MotoTech)]

I bought some used ones from here/the original site.

I'll have to measure my carbs and see what size they are.

[SoCal250]

These carbs bolt right up: https://www.summitracing.com/parts/mku-vm20-273
to Yamaha manifolds 314-13565-00-00




Here's an example:

[JKV45]

These carbs bolt right up: https://www.summitracing.com/parts/mku-vm20-273
to Yamaha manifolds 314-13565-00-00




Here's an example:

Those look pretty nice - and $150 ea isn't bad.

I didn't realize that Yamaha used cheap-o carbs (TeiKei) on any of their small bikes.

[X-Man]

Those looks awesome. I wish I had done that with my RD125's I had. Sold them because of the carbs.

[Sleeper217]

Curious how you reached that conclusion.


Thank you for responding to my post.

My conclusion, more like an acceptance, stems from the fact that the original carbs I have are in disastrous shape and parts are hard to find.  In addition, for my purposes and intentions for the bike it would be more economical and practical to go with aftermarket carbs.

I would talk to Gordon from Custom Carb Service (https://www.customcarbservice.com/) before buying new carbs.

You could send some photos and specs, and see what he says.  I've known him for quite a while, and he is a straight-shooter and very detailed.  He will let you know if they are not usable or repairable.

Gordon is well known for saving plenty of really bad Ninja 250 (among many other) carbs. The photos on his main page show some good examples of before and after.  There are some really bad before pics.

Thank you for the information.  I'll keep it in mind.

Cheers!

[Sleeper217]

The OEM TeiKei carbs on the RD125 are crap. Poor design, hard to get parts (jets, etc.). Yamaha only used the TKs on the  RD125 & RD200. If yours are damaged or missing parts there's no sense in trying to resurrect them especially if the bike isn't all stock. The only reason I'm still running them on my RD125 is that it's 100% original and a multiple show winner, otherwise I'd upgrade to Mikunis in a heartbeat.

Because the TeiKeis have an integrated angled flange anything you upgrade to will need new flanges to adapt them so the new carbs sit level. You can use Yamaha OE manifolds from a CT2 or DT125A and then bolt up flange-mount Mikunis, like VM20-273. No difficult mods involved, just have a custom lower throttle cable made.

I wouldn't go too large on the carbs especially if you're not building a hotrod engine or you may run into performance issues. If the throats are too large you end up losing velocity causing atomization problems with the fuel charge. Since the OE carbs are 18mm I'd try to keep it at 20mm, which is the size used on the 200. One of my many projects down the road is to get my second RD125 going and the tentative plan for that one is VM20 Mikunis on DT125 manifolds (already have the manifolds in my stash).

Thanks again SoCal250! 

My plan for this project is a road going, reliable ride with a little extra pep.  Retain autolube, swap points out for electronic ignition and aftermarket pipes since mine aren't salvageable.  Thank you again for the input.  All great feedback!

Cheers