Vintage Dirt Bike Q & A

I have a CR 125 M. I am trying to get this bike running. I have to get a new piston and bore it. But also I have a problem that is unusual I have been unable to locate the right carb. but I have located a CR 125 R carb. and (cable w/slide). If someone has a CR 125 M carb. (cable w/slide) I will trade straight up. Unless I can use the CR 125 R carb. on my CR 125 M with out any problems does anyone no if this will work. Please help I want to get this bike going. Thanks.

What year of CR125M do you have, and what year of CR125R is your carb from? The '76-'78 CR125M's used a different carb and manifold from the early ones, and the CR125R's were all over the place.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Believe it or not. I have a '78 cr125M and my carb came off a '79 cr125R. It fit the intake boot if I remember but the bowl sat alot lower than the one I need (from the pics anyway). The R has reeds someone told me and the M doesn't so it won't work. Or will it I actually got the bike to idle with the R carb by some strange miracle if you want to call it that but it would die immediatly when you give it to much gas or try to take off. The bike also needs new rings and probably a piston since my compression test is very low. So I (ass)umed that this was my problem till I asked and someone told me it wouldn't work even if the engine was in good shape. Don't even ask me how I got it to even idle I still don't know.

Your '79 CR125R carb should work fine on your '78 CR125M; in fact, the stock jetting should be pretty close as-is. Your bogging problem is almost certainly caused by the low compression, unless the carb passages are clogged - but it really doesn't matter, you should definitely fix the compression problem before starting on the carb. Engines with very low compression will usually have enough power to idle and rev without a load, but that's about it.

I have a '78 CR125M carb, that's going on my MR175. It's a 30mm Keihin with a shallow float bowl. I believe the '79 CR125R carb is a 32mm Keihin with the deeper float bowl, as you mentioned. As long as it fits the intake manifold and the air filter boot, the cable works, and the carb is clean and working properly, you should be good to go.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric