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I have looked for {model} carb, I have searched the numbers and letters stamped onto the carb, and I finally resorted to measuring it to just try to find a compatible one based on the size (28mm for instance), however, I found too many results (all different from each other) with the first method, none with the second, and several with the third - all of which were the right size in one or two places, but never the correct distance for the bolts, for instance.

Why is it all condensed down to a single specification like 28mm or 30mm? What measurement(s) don’t need to be the same to still be compatible?

I know this is a basic question and yes I have searched. I must just not know the right words to be using, because I know this has to be one of the first lessons of working with carbs and I’m sure this is a duplicate; I’m just not able to find that dup question and the associated answer by myself any better than I seem to be able to find a replacement carb… here are the images I am basing my search on:

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    It would help if you would include the make and model of your motorcycle - that is far more likely to help identify it than just a measurement
    – Rory Alsop
    Jul 25, 2022 at 8:02
  • Carburetor inlet throat diameter are sized for the engine displacement and expected power for all around performance including fuel economy. Are you familiar with carburetor operation, maintenance and repair? If not severely worn out, carbs can be rebuilt to restore it back to factory function without buying a new one.
    – F Dryer
    Jul 28, 2022 at 21:54

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There is not really any "standard" as far as carburetors are concerned. This appears to be a mass-produced bike and in that case it's quite possible that the carb is a custom one that is made for just this make/model of bike. In some instances a carb may be shared among several related models but that is not a rule by any means.

At times you may find that there are similar carbs that can be used to replace the original ones but usually you will need to do some modifications to the carb, the bike, or both to make things work properly. There may also need to be some trial-and-error until you find the correct combination of carb, jetting, and other adjustments to get the bike to run properly.

If you are trying to locate a replacement carb for this bike, your best bet is to use the manufacturer's parts fiche to find the correct part number and then see if it's still available as a spare part or look to one of the vintage bike parts sources that are out there.

From this view is appears to be a Keihin:

Image

Are you sure there is not a Keihin model number on it somewhere?

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