Vintage Dirt Bike Q & A

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PostPosted: Sun Jun 04, 2017 9:02 pm 
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Joined: Wed May 31, 2017 7:05 am
Posts: 3
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.

Thanks.


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PostPosted: Mon Jun 05, 2017 6:24 am 
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Joined: Sun Nov 30, 2008 12:10 pm
Posts: 1004
Location: Connecticut, USA
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.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric


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PostPosted: Wed Jun 07, 2017 9:06 am 
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Joined: Wed May 31, 2017 7:05 am
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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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