Vintage Dirt Bike Q & A

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PostPosted: Mon Jan 26, 2004 9:22 am 
I have a 76 125 that I am having some issues with. I have rebored the cylinder and put in a new piston. I have replaced the clutch plates. The bike starts up great idles good, and shifts fine, but when I let out the clutch in first the rpms drop and the bike nearly boggs out and stalls unless I am revving HIGH rpms. I thought it was a bad clutch but since I have replaced the plates I don't think that is it. Could it be the carb? Anyone else have this problem?


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PostPosted: Mon Jan 26, 2004 9:23 am 
I have a 76 CR 125 with the stock Keihin carb. It is a very pipey 125 and you have to rev the hell out of it. I race it in the Rocky Mountain Postvintage AHRMA series; it is about 5000 ft. above sea level here. I have the carb needle clip on the top position. You may want to check yours and drop the needle to lean it out a bit. I tend to run the main jet rich because it is such a screamer bike, and I mix Suzuki CCI oil at 20:1. Since I switched to CCI at that ratio I have never had any top end or rod failures. I strongly suggest you try to jet your bike correctly and mix a good oil at 20:1. Then ride it wide open!


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PostPosted: Mon Jan 26, 2004 9:44 am 
Every CR125 I have ever ridden has a high top-end power band. That is why honda has the most moto wins ever. The guys that can hold'um WFO are the ones who win. If you play ride you can lower the teeth on the rear sprocket. Or more teeth on your drive sprocket. That will give you a little more lower end torqe to get the bike going.


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PostPosted: Mon Jan 26, 2004 9:44 am 
That sounds like the same problem I had with my 76 CR 125. My bike would do that until I learned that you have to rev the piss out of those bikes to get them to work properly. As long as it runs fine at high rpm than that should take care of it. Hope that helps.


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PostPosted: Mon Jan 26, 2004 9:45 am 
Thanks Jon,
It does run great at High RPM's but I wasn't sure if this was how it should be. I just had the cylinder rebore and a new piston put in so I didn't want to redline it and cause another sezure!


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