Vintage Dirt Bike Q & A

Carb Guidance 1977 CR125m
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Author:  dutycat [ Sun Jun 04, 2017 9:02 pm ]
Post subject:  Carb Guidance 1977 CR125m

Ok folks, Greetings.

I am restoring a 1977 CR125m and I am not sure what carb it came with. Some say 28mm. Some say 30mm.

I am looking at putting Mikuin 28 on it, and I am curious if anyone has any jetting guidance for either a 28mm, a 30mm, or both. It currently has a 32, and aside from it being too pipey, there may be some other issues.

I am experimenting here, and will get it all worked out eventually.


Author:  rayivers [ Mon Jun 05, 2017 6:24 am ]
Post subject:  Re: Carb Guidance 1977 CR125m

The original carb is a Keihin 30mm, stamped 083A on the LH side. IMO it's not the greatest carb, but it works OK at large throttle openings. The OEM jets (140 main, 45 pilot) are probably decent starting points. The small-mouth Keihin 28mm has better throttle response at all throttle openings, but less peak power.


Author:  dutycat [ Wed Jun 07, 2017 9:06 am ]
Post subject:  Re: Carb Guidance 1977 CR125m

I have a 28mm Mikuni coming, not a Keihin. Best guess as were to start with it? It comes with a 200 main jet. The previous owner said that the 32mm on the bike now ran best with a 280.

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