Switching from a Kehin PJ to a PWK air strike

[Big Daddy]

I have a 1998 CR 125. The stock carb is a 36MM Kehin PJ, I'm buying a 38MM Kehin PWK Air-Strike to replace it. My bike has an Rad Valve and a FMF fatty pipe and 1999 CR 125 air tube. I'm currently running an 48 pilot jet a 1468 needle in the 4th slot and a 162 to 165 main jet.

What would be the guess on the new jetting specification???

I what way will the carburetion change?

 

[Big Daddy]

Can any one help?

 

[James]

The change MAY be a bit more rev up top and some loss of low end responsiveness. I think Marcus had a thread on this somewhere.

Like the jetting, you won't really know the change til you put it in there and try it.

 

[marcusgunby]

I used a 38mm Mikuni on a 01Cr125-i have no idea of jetting for your mods -sorry.

 

[bclapham]

did any of the ktm125's run a 38mm before they went to 39.5mm? that might be a good starting point.

other than that, all the 125s are running the tmx38 or tmx38s so that makes life hard. what about looking at what a 2000 cr250 used in the stock pwk38 and extrapolating???

 

[marcusgunby]

The KTM has always ran a 39.5mm.The KTM jetting might be a good starting point however.

 

[James]

the 2000 cr250 used a 180 main and a 48 pilot. I am not sure if the needle is specific to the CR but I'll be glad to get the number off of it if that helps.

So now what I am curious about is....logically....would 125s require larger or smaller jets in general due to the smaller displacement?

 

[bclapham]

Originally posted by James
So now what I am curious about is....logically....would 125s require larger or smaller jets in general due to the smaller displacement?

i would say bigger jets since it isnt drawing as much air, but i am only going from the examples put forward to me with respect to building a bigger bore.

however, the next time someone brings a rulebook on these things to me i shall beat them with it! :p :)

 

[marcusgunby]

Alot of the time the jets are very similar apart from the needle and slide which are leaner on the 250s.

 

[Big Daddy]

I tried the new carb tonight. 50PJ 1368N Needle and a 168MJ. It had more mid response and top end. Low end is a little weak compared to the PJ36mm.
Pulled the choke and it ran a little better out of the burms. I think I'll try a 1468N needle next time I have the carb apart. The taper is 1/4 degree richer.

I think I'm getting close.

 

[bclapham]

just want to bump this one to the top, big daddy, what slide did you use? i have the 38mm pwk on my rm144 and cant get it to run- major bog on quick throttle movements-

 

[Big Daddy]

bclapham
I had a heck of a time tuning my cr125. First I must tell you that I added a Power Now and was trying to jet that also. My best setting with Power now was 35 or 38 Slow Jet which was still to rich at idle. A #7 slide. DDE(1464!) needle in the 3 clip with a 165-168 Main Jet. This gave me the same low end as the PJ36 but came into the stronger midrange very quick with one pull of the clutch. The top end was alot stronger. Big diference. Pj's seen to respond better to a steeper needle angle. PWK's seen to respond better to a smaller needle diameter. Going from a 1370 to a 1369 would be a joke, you should atleast 2 or 3 sizes to see a big diffence. I don't know what the best setting's would be without the Power Now. I put the PJ back on and traded it in for a 2003 yz250. The Power now fits the 2003 yz 250! The little fins on the PWK a/s suck the fuel at idle but does nothing for fuel pick up at 1/2 in my opinion. I must say the little 1998 cr125 ripped for what it was. (38mm PWK A/S for sale now)

 

[bclapham]

thanks bigdaddy!