All 2st Throttle mod from Mikuni nr4 to nr5.

Hello guys. My son has a WR 125 2008 and he has my Mikuni TMXX from my 300 on it. We use the CHY needle in it, and it,s a bit rich in the middle, and it cuts out the sparkplug if he doesn,t clean it out every now and then. I have needle in leanest clip so i have thoughts of modify the throttle to a number 5. Does anyone know how deep the cut is on the nr 5 throttle compared to the nr4?

number 5 is leaner 0>1/4 throttle you can grind back using a small flap sander in a drill press, but will not effect 1/2 throttle for that you will need smaller main or fatter needle.

Yes, i know the jetting principles, but when he is using very light throttle in the woods it clogs up. i would prefer to use a needle that is slightly less tapered likeCFY16-62 instead of CHY that bludders at middle throttle too. The question is how much i should cut off from the throttle.

Johnny

ok, i thought your prob was mid throttle, i would try a number six or grind out your number four approx 1mm all round as per above you can always raise needle if you find it too lean.i have a 25 pilot in my tmx and wii be going even smaller but high temperatures here.when i get chance i am going to do some experiments with needle profiles in relation with pv and throttle opening positions.hope this helps, good luck .

john

Ok, so 1mm is the right amount then? I have the needle in leanest clip at almost zero degrees and it,s still too rich. I,ll try to file it a bit. Thanks!

Johnny