This may have previously been covered, so I apologize in advance if I'm wasting your time.
I have a 2004 CRF250X. This is the California edition with the smog pump installed. The air box was cut by the previous owner, and the 250R exhaust was installed. I was unaware of this until last week, but the carb was never rejetted after the air box was cut. When riding, I would experience some major sputtering and power lurches around 2/3 or 3/4 throttle. I learned to live with it, but it has always bothered me.
Last week I decided to do something about it. So I bought a JD Jet kit for the bike. I pulled out the stock needle (with the clip in the 2nd position from the top) and I removed the stock 130 main jet. I installed the red JD needle with the clip in the recommended 5th position. The stock 42 pilot was what JD recommended, and they said to put in a 160 main jet. Since everything I have ready about these bikes says they are jetted lean from the factory, the recommendation made sense. But when I took it out for a ride, the sputtering and loss of power was worse than before I did the rejetting, and it would start sputtering around half throttle. It was almost impossible to ride! So I pulled the needle out and went to the 4th clip. The sputtering got a little better; I could make it to about 2/3 throttle before it would sputter and lurch. I tried a 165 main and a 158 just for the heck of it to see if those would help...with no luck. It doesn't matter if I snap on the throttle or slowly roll on it, it happens around the same spot every time. Do I need to go to the 3rd clip on the needle and give that a try?
I am in the Dallas/Fort Worth area (around 500' elevation) and ride in temperatures of 70-100 degrees F.
Thanks in advance for the help.