I put about 4 hours on my TX300 before I touched the jetting. Figured I would leave it rich for the break in. I decided to do the slide mod to it that many people have done to help clean up the Mikuni at the time I changed the jetting. To my surprise when I went riding this week, the bike ran much worse. Was horribly rich. I had planned on putting a JD jetting kit and a V-Force reed block in it at some point so this made it happen right away.
I found the root of the problem when I installed the new parts.