[chris_arend]

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.

[Leardriver]

Is it possible that the carb is clogged somewhere? Those settings should work well enough.
The base rule for the main is to pull the choke out while riding, and see if the top end is better or worse. Remember, the main only affect 3/4 throttle or more, so the top end.
If giving it more fuel works, then you were too lean. Now, you aren't too lean with a JD needle and 160 main, so if it is sputtering, you have a restricted passage somewhere.
These things have a way of solving themselves if you are going to ride it a bunch.