The only "wear item" in a Mikuni carb that can't be easily be brought back to brand new spec is the throttle slide in the slide bore. Even though these bikes are old, most have low miles and I can't say I've ever seen a Yamaha with a slide and/or slide bore worn to the point of being loose.

Most people just want to throw carb on and have bike run good...  in my experience sticking with stock carb is the easiest way to do that.  Back in the day I know of only one company that sold replacement carbs (usually larger, but not always) that took the time to painstakingly choose the best needle profile and jetting like OEM did...  Klemm Research.  Generic carbs often run okay but few people are willing to spend the time and expense to swap needles and jets to dial in the jetting like the factory did.  (And if you buy Chinese knockoffs sometimes you can't swap jets even if you want to)

A big problem with 50 + year old carbs is getting parts for them, which in many cases were manufacturer specific.

Something like a Nibbi Keihin PE clone, with a JJH needle, and jets of similar sizes to the OE carb, is very likely to work great, and costs about $60.

I highly discourage using aftermarket carburetors especially from China on Yamaha Enduro’s. MarkT is being nice. I toss them all in the garbage can at my shop and never try to tune a bike with anything other than OEM equipment.

asco….

If parts for OE carbs are still easy to source, and there is a want to retain an original appearance, keeping the original carb is fine.

The $20 Chinese carbs are very poor, and these probably mean all Chinese carbs being seen as just as bad?

My $20 Chinese 28mm on my 175--that turned out to be about 26mm unfinished in the venturi actually works perfect with a bit of jetting of the main. [just saying] & stirring the pot lol--like an oil thread.

Speaking from experience, many times a modern carb has different physical dimensions than the original...  so often you're stuck with not being able to use the original air filter arrangement.  Cables are another common "pain point".  Very often the original throttle cable does not work with a new aftermarket carb.  And with the splitter and autolube this can be a hassle unless you have the supplies and know how to build a new cable or can modify the existing one.

And again, a carb being "old" doesn't mean squat.  Especially a Mikuni.  Rare to have something wear out.  I have two 1964 Yamaha's that have had their carbs cleaned multiple times and are still using all the original parts...  including the float bowl gasket. 

And if you do need a Yamaha Mikuni part most jets are still used today and can be bought from Mikuni... and the few that aren't often have equivalents or can be found on ebay.   

I didn't say all Chinese carbs are bad...  all I said is they can be a crapshoot and some have oddball jet threads or pressed in jets so you're stuck with whatever the carb came with.  I have a friend that bought a $20 Chinese carb for a CT1...  it ran darn good. Jets were the same thread as Mikuni.   About six months later he bought the same brand and model $20 carb from the same place for another CT1 he had.  That one didn't run very well at all and the jets were not replaceable.  Seller wouldn't take it back because it had gas run through it (Federal shipping law was quoted which is true).  In the trash it went.  I cleaned his original Mikuni for him (no parts needed replacing) and that bike runs great now too.  Last I heard the first bike with the $20 carb is still running just as good as the one with the original Mikuni. 

I know others that were missing a carb or just wanted a new one and they had good luck with the Chinese carbs...  a few didn't.  It's kind of a "roll the dice" thing from what I've seen.

Those were all early AT/CT carbs...  once you start talking other models or later years you often get into physical fitment issues and cable issues. 

 

If you pay $20 for a Chinese made carb, that's exactly what you get. About 3 years ago, the Taiwan OKO carb brand was sold to the Chinese. Made in China OKO's are now a budget brand, and are available for as little as $18.

Some of the very cheap carbs work fine, but quality control is sketchy, and many of them have faults. If you pay more money for a Nibbi, then you have a carb which isnt that far away from Japanese.

Keihin clone carbs have an air box stub diameter between 43-48mm, so a step-down adapter will be needed to fit one on a bike whose OE carb had a smaller diameter air intake.

In regard to OE carbs, the parts that wear, such as needles, needle jets, float needles and seats, are difficult/impossible to find here in the UK, and even some carbs such as small body Thailand VM Mikuni, have not been available for quite a while.  Manufacture of PE26 Keihin's has ceased completely.

I took a photo of the two needle jets. the one the right is the one that was giving me issues. it does show significant more wear.

I did find a source for a nos jet and ordered a new needle.   I will update when those are installed.

 

Thanks for the update. Be interesting to see how it goes. Hope the needle & jet are a match pair even though bought separately--numbers match with specs etc.
Pics do show a difference if both started off the same & same numbers.
The severely worn ones i'm used you can eyeball the elongation.
Farm quad excessively worn ones might've been because of being 4 stroke they pulse back & forth at cow following slow speed a lot more.
In those the needle was alloy. Later replacements came either made from stainless or were plated. Needle still alloy though--i guess some high tensile alloy not soft stuff.
Hope it sorts your problem.

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