Hi 

I am looking for a carb for my 76 C top end. 
Stock was a 30mm ss I believe but you can't buy those new anymore. 

Looking on MikuniOz  (where I buy my new carbs) they have 32/34s, the X ran a 34 but obviously had different porting. 
Don't mind going aftermarket like a pwk ect. 

​​​​​​Has anyone ran anything other than stock? 

Thanks 

It's probably important to note that I'm sure you're talking about the YZ 125C and not the garden variety DT 125C enduro this forum caters to..

Hard to find a small body 30mm anymore these days. 28mm would probably fine for street use.

YZ125X manifold had a bigger opening for the medium body carb so if you want new and bigger than a 28, you should consider the "X" manifold.  Porting wasn't that much different as stated in article I sent you...  they recommended a 32mm if I remember correctly.  (X model actually has too high an exhaust port so C is better.)

Thank mark. 
Yes sorry yz125c.. 
It was hard enough finding the C manifold locally. So il keep with that for now. 

28mm is probably a good idea. 
 I can then use that on my 125a if needed also. 
 You don't have 28mm carbs spec on hand that would be a good starting point for jetting ect on the C? 

Kind regards 
Marcus 

Try the Mikuni VM30-83 you can find it at Niche Cycle, you will need to jet it based on your bike.

I don't have specs...  but generally the jets a Mikuni comes with are fairly close.

As far as "Try the Mikuni VM30-83 you can find it at Niche Cycle, you will need to jet it based on your bike"  unfortunately that's a medium body Mikuni and would not fit the "C" manifold...  you'd need an "X" manifold.  

 

You, still, can go to Niche and they have charts with the dimensions and you can find something that fits your YZ125C, the original carburetor was a Mikuni VM30SC, other option is eBay, the VM30SC was a common carburetor for other motocross bikes.

@luisarreola, Niche is one of my favorite Mikuni places!  VM28 is the largest small body Mikuni you can readily get new. 

I'm not sure how many MX bikes used a small body 30 back in the day... Yamaha did use a small body 30 on a couple 125 models around 75-76...   but I've never had much luck finding one on ebay or anywhere else...  except the occasional beat up used one for $300.   I wanted one for one for a "sleeper" DT175 I'm building... almost have all the parts and hopefully can assemble soon.  Need to make room to work first.

In about 1976, I'm pretty sure Yamaha moved to the "medium body" carb for anything over a 28. So I think it was only a couple Yamaha 125 race models that got the very special small body 30. 

Then I finally scored a small body 30 in a bin of miscellaneous Yamaha parts that I didn't even know contained carburetors!

It's possible I just didn't know what to search for...  and maybe a vintage small body 30 is more available from other brands of old bikes?