1990 KDX125 strange jetting problems!

[KDX125A]

Hi guys,

I have recently fitted a Pro Circuit expansion pipe from a 1990 KX125 onto my KDX125.

It took a little bit of fab work but I managed to get it on there...

So now I know I have to rejet (which I have been doing) but I am running into strange issue. I was running a Big One / Fresco expansion but it was pretty dull to say the least and my goal is to try and make it as quick and reliable as possible.

I am running a Polini PWK30 flat slide carb and had it jetted pretty good with the Big One pipe, however now with the PC pipe I am getting misfires or stutters past 5/6k.

I have bumped the main jet up from a 130 to a 160 & checked the plug after any adjustments made and it still look very clean!

Is it possible that I am still lean even after bumping the main up that much?! The plug still seems VERY clean after a 5/6th gear pull.

Thanks guys!

[bufftester]

As with any jetting, you need to start with the pilot first. The PJ is in play 100% of the time and is why you need to set it first. Changing anything in the intake/exhaust tract requires you to go through the ENTIRE jetting procedure from the beginning.