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05 to 07 CR125 Jetting Questions,...

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Picked this bike up a while back, made it a project, 05 CR125, I just put a new Wiseco topend in it, still on stock bore, I am at sealevel elevation, my jetting is 35 on the pilot jet, 420 on the main with c-clip on the third down. I have the air screw set on 2 turns out for crisp throttle response on every gear, my question mainly is, when I first start it up it has a pretty high idle even with the choke on, after about 35 to 40 seconds or so it slowly idles itself down to a near perfect 4- stroke idle. Should I up my pilot jet one size? I've have tried lowering the c-clip one position richening the mixture and it doesn't really make any difference, still a somewhat high cold idle but with the clip moved down one position it loads up when riding unless on the pipe. New foam air filter and airbox freshly re-sealed so no air leaks at all anywhere, Boysen reeds are also perfect. I also premix at 32:1. Any of you guys familiar with the jetting on these bikes, still not really sure what is supposed to be normal. Thanks.

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Many of us are familiar.  Stock mikuni carb is pretty worthless.  You can get it dialed in, then the sun might go behind a cloud and  5 minutes later foul a plug.  Best option is to replace the carb with a 2001 or newer YZ250 oem pwk.  Many threads on TT specifically on this subject.  Needle options continue to evolve.  I have several workable jetting setups.

 

http://www.thumpertalk.com/topic/879109-pwk-conversion-infomation/

http://www.thumpertalk.com/topic/1044850-cr125-needles-pwk/

http://www.thumpertalk.com/topic/978692-38-pwk-as-in-a-02-cr125/

http://www.thumpertalk.com/topic/1013742-keihin-pwk-airstriker-yz250-to-cr250-“starter-kit”-w-harness/

http://www.thumpertalk.com/topic/844273-tps-measurement-on-a-06-cr125/

 

good luck.

Edited by magpie5
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I think I just figured this out. The CR125 service manual is wrong. The CR250 service manual is correct. Both bikes use the same TPS, part number:

16060-KSR-732

See screen shots below. The 125 manual incorrectly states Yellow/Red, Yellow/Blue for the variable 0-5 ohm test. The 250 manual correctly states Blue/Green, Yellow/Blue for the same test. Same test, for same part number. :thumbsup: This corresponds with the short body PWK color codes for the same TPS variable ohm measurement, i.e. Black & Yellow.

You may run into this.  Reference quote.

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Thanks for the info, have you tried a JD jet kit? I have used them on several other bikes that I was at the point of ready to sell before I installed his kit, it literally turned it into a love story, kit was phenomenal on every bike I have put them in.This will be my first choice rather then trying other carbs, that is a very expensive risk without something set in stone to go by.

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Thanks for the info, have you tried a JD jet kit? I have used them on several other bikes that I was at the point of ready to sell before I installed his kit, it literally turned it into a love story, kit was phenomenal on every bike I have put them in.This will be my first choice rather then trying other carbs, that is a very expensive risk without something set in stone to go by.

Yes I tried the JD kit on my 05 CR125 with the stock mikuni.  The kit does improve the jetting from the stock pig rich condition that the bike comes in.  However, I would still consistently foul plugs, just slightly less frequently.  And nothing was wrong with my bike.  I exchanged the kit and put one of JD's pre jetted pwk on my bike and never fouled a plug again.  JD's needles are good, however there are other needles that are just as good and much less expensive.

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I've probably got a couple hours now on my bike since I did the piston and ring as well as a whole new clutch pack and It has never fouled a plug yet. Jetting all around feels perfect, clean and crisp but just seems like to high of an idle at cold start up, i'm old fashion and swear by a heavy 32:1 premix, I use Klotz techniplate full synthetic, just don't want to shorten ring life due to the high idle starts. Think i'm just gonna try one size larger on the pilot jet and see how she does for now.

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