Motorcycle Repair: 2002 kx 125 jetting, air screw, pilot jet

Question
I have a 2002 kx 125 kawasaki, its stock except a fmf fatty pipe, 170 psi compression i bought it in Denver colorado, and it was jetted for around 8 to 10,000 feet, i live at 4000 feet, it is a mikuni tmx 38 series carb, the (stock) jetting is 350 main, 45 pilot, middle clip position, 5.5 slide, air screw 1.5 turns out,the needle is stock, when i brought it home and rode it it had a slight bog on the bottom end and then ripped thru the mid and top, the plug looked like new and no spooge anywhere the inside of the pipe was grey and very dry,here is what i found inside the carb, the float was a 2 mm high, main jet was 270, pilot was stock(45) slide was stock (5.5) needle was dropped 1 clip(second from the top) air screw was about 2.5 out, i use amsoil at 50/1, the bike is lean , and im just wondering if the slight bog on the bottom end is a lean bog?, any suggestions on where to start with the jetting?  I was thinking of going with a 310 main, 40 pilot,stock slide, stock needle in the stock clip position (3rd) and adjust the air screw accordingly, do you think at my altitude 4000 feet i could get away with the stock 45 pilot? Thanks for the help...bill  

Answer
Hi Bill,

Based upon a temperature of about 68 degrees F, and about 3,500' above SL, my calculations indicate working with the air-fuel screw and the following jet sizes:

#255 main jet

#42.5 or #45 pilot jet

I could be more specific if I knew your average environment temperature. There are many variables when tuning air-fuel mixtures. : )

In any case, make one change at a time to know what effects each change has made. Too many changes leads to wasted time.


Respectfully,
Mark Shively
Dayton, Ohio