You are on the right track, but without an exhaust gas analyzer and a dyno, you are going to have a bit more of a difficult time zeroing in on the problem.
Nonetheless, i would drop the needles one notch, (may not be possible depending on where they are.. you may have to move clips or get adjustable needles) If you cannot drop the needles i would recommend dropping the main jet size by 2 or 3 (example: if you now have "105" main jets, change them to "102")
This will lean out your mixture and you should see a difference.
Performance MAY go up or it may go down.
Also, you should check your air filter, as a dirty air filter can cause similar problems and effectively richen up your final mixture.
This is all standard troubleshooting steps. Its hard to say exactly what the problem is with the limited info given.