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jetting/tuning for rad valve/pwk on cr125

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(x-post from technical forum)

 

Looking for some starting points for jetting for a 01 cr125 with a 38mm air striker with the intentions of adding a boyesen rad valve.  all jetting recommendations are for the stock 36mm tmx carb. 

 

Currently at 182 main, 45 pilot, 1.75 turns on a/s, 5.5# slide and N3CG needle.

 

According to boyesen for stock 01 cr125 they suggest leaning out the main 2 steps and leaning out the slow jet 5 steps.    for a cr250 (where the carb originated) only leaning out the main a few steps but leaving the slow jet alone).  

 

Curious to hear what others have done as I can seem to turn up anything by searching around and to my understanding the rad valve will run just fine without jetting change but to really see benefit you need to jet accordingly - I just don't know where to start or which way to go. 

 

Thanks!

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Having used a rad valve on my 94cr144 with the 38mm pwk on it, I would say to just leave your jetting alone.  You already seem a bit lean on the main jet as it is so I would imagine that going leaner would not be a good idea. 

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Having used a rad valve on my 94cr144 with the 38mm pwk on it, I would say to just leave your jetting alone.  You already seem a bit lean on the main jet as it is so I would imagine that going leaner would not be a good idea. 

 

Definitely not lean, fouled a plug real fast today almost to the point the bike couldn't be limped back to the truck (within 15-20 minutes of moderately hard trail riding) - my bike never fouls plugs. so I dropped the main 2 sizes (now at 178) and it was a bit better but still isn't 100% and I haven't been able to do a proper chop yet.

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Definitely not lean, fouled a plug real fast today almost to the point the bike couldn't be limped back to the truck (within 15-20 minutes of moderately hard trail riding) - my bike never fouls plugs. so I dropped the main 2 sizes (now at 178) and it was a bit better but still isn't 100% and I haven't been able to do a proper chop yet.

 

k, so when I was using the PWK on my 94 144, the JD blue needle was what I was using.  I had been told by RTV that the N3CG needle is a really good one for my 144 but was never able to try it out.  My configuration was a 182 main, needle clip in the 4th clip position, the #7 slide with a 45 pilot.  I am at 4300 feet above sea level.  That combination ran really well on my bike.  I did a needle comparison with JD's Tuning guide spreadsheet and here is my observation.  The 5.5 slide is probably too rich for you with that needle. Maybe a 6 or 7 slide would be a better slide for you.  Second, 178 is really lean especially on a 125.  IMO, you have a mechanical problem if you are at 178 on your main and it is still running rich.  Have you pressure tested the motor?  Is your piston and ring fresh? 

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k, so when I was using the PWK on my 94 144, the JD blue needle was what I was using.  I had been told by RTV that the N3CG needle is a really good one for my 144 but was never able to try it out.  My configuration was a 182 main, needle clip in the 4th clip position, the #7 slide with a 45 pilot.  I am at 4300 feet above sea level.  That combination ran really well on my bike.  I did a needle comparison with JD's Tuning guide spreadsheet and here is my observation.  The 5.5 slide is probably too rich for you with that needle. Maybe a 6 or 7 slide would be a better slide for you.  Second, 178 is really lean especially on a 125.  IMO, you have a mechanical problem if you are at 178 on your main and it is still running rich.  Have you pressure tested the motor?  Is your piston and ring fresh? 

 

7 hours on brand new top end - ran spot on perfect jetting with those specs prior to rad valve crisp morning toast brown on the plug, no bogs anywhere throughout the range.  yesterdays ride extended into the evening hours (dropped a solid 15-20* from the day time ride temp) bike woke up a bunch and was much more punchy/wheel lift-y leading me to consider that it's still a tad rich - might try adjust for that richness on the needle.

 

I appreciate your consultation 🙂

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On my CR 125 (with Mugen equipped HPP engine), i use the following carburetion with great results. I tried JD jetting kits and other needles but nothing was as crisp in my PWK as the one below (or the one i use in my older 38 PJ carburetors):

 

38mm PWK AS

Main:185

Needle: N3CG (middle)

Slow: 42

Slide: 7

Air: 2

Edited by nino
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 Second, 178 is really lean especially on a 125.  IMO, you have a mechanical problem if you are at 178 on your main and it is still running rich.  Have you pressure tested the motor?  Is your piston and ring fresh? 

crud, was peeling mud off the bike tonight getting ready for the weekend I noticed the air boot wasn't settled right on the carb (effectively constricting airflow) looks like you may be on point with the lean main, fixed air boot and put in a richer jet in preparation for proper air flow from filter.  I don't know when the boot fouled up could have been from the jump (poor installation when i put  in the rad valve) or when I lowered the jet this past sunday during the ride.  Plug looked boarderline lean so richer for now it is.

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crud, was peeling mud off the bike tonight getting ready for the weekend I noticed the air boot wasn't settled right on the carb (effectively constricting airflow) looks like you may be on point with the lean main, fixed air boot and put in a richer jet in preparation for proper air flow from filter.  I don't know when the boot fouled up could have been from the jump (poor installation when i put  in the rad valve) or when I lowered the jet this past sunday during the ride.  Plug looked boarderline lean so richer for now it is.

 

 

That would definitely cause more vacuum through the carb and make it so your jetting could foul a plug.  It was a good idea to richen up your jetting.  The jet specs that NINO posted with that N3CG needle would be very good settings to follow.  IMO, you should look into the #7 slide.  The only thing I would suggest is to start with a 45 pilot and then lean out to the 42 if needed since European gas is different than USA gas.  

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