CR125 bog...kind of

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5/7/2018 1:27 AM

This forum has been super helpful with my kx250f and now I have a 2003 cr125 thats giving me a couple issues.

The bike starts up just fine but once running it has a somewhat rough/fluctuating idle and a "bog" at high rpms. I changed the jetting from 430/30 to 390/37.5 and I set the clip to the 2nd clip down on the needle. When giving it full throttle it kind of bogs towards the high RPMs and almost kind of clears itself out after a second or two if that makes any sense. As far as the idle its never really steady and fluctuates. I just ordered new crank seals for either side which I've heard can be my issue but aside from that where else should I start? I was planning on tearing into the exhaust to make sure it isn't plugged and gummed up and the same with the power valve but I haven't gotten to them yet. Looking for some input first.


5/7/2018 4:57 AM

The air boot can be the cause of air leaks too.


5/7/2018 8:01 PM

I took the exhaust off and the power valve cover off today and the exhaust had some carbon build up but nothing crazy. Also the power valve seemed fine and didn't appear gummed up or anything. I don't think replacing the crank seals are going to fix my bog issue at higher RPM but I guess we will see. I did a compression test and I only have 110psi, I think its time for a new piston and rings too.


5/8/2018 10:30 AM

Hmm, that does seem lean settings you went to. I'm in CA for near sea level to 2000 feet usually. I had my 03 with the following jetting
430 main
40 pilot
2nd clip 5.75 slide


5/8/2018 4:13 PM

seth505 wrote:

Hmm, that does seem lean settings you went to. I'm in CA for near sea level to 2000 feet usually. I had my 03 with the ...more

What is the 5.75 slide?

I used the recommended jetting specs from Pro Circuit, but the bike ran the same either crap. Im going to install new crank seals and go from there, if that doesn't do it im going to do a new top end and if that doesn't do it then I will be at a total loss.


5/12/2018 5:55 PM

Little update:

I replaced both crank seals, the right side (wet seal) had a small chunk of the inner seal missing and the chunk was on the actual bearing. The metal ring was also out of the seal when I popped it off. With both replaced it idles way better but I haven't gotten a chance to really ride it or rev it up too high (trying not to make my neighbors hate me). It also appears to be smoking less so maybe a top end is still in order.