I just got my Logitech G27, and I try to play on a configuration kart racing pro.
I have a problem with force feedback, when I put on the games and the logitech profiler, my steering wheel starts to shake terribly in games
Sorry for my English ...
You are not alone with this problem, my G25 does the same. Look here for a discussion about it: http://forum.kartracing-pro.com/index.php?topic=596.0
I got used to it, so it's not a real problem for me anymore.
For a wheel setup in KRP you can also look here: http://forum.kartracing-pro.com/index.php?topic=915.0
Try them and choose the one which fits best to you.
I have a G27 setup also. You might want to try setting the Force Feedback Strength to ~90% and Dampening to 0%. This minimized the thrashing at least in KRP Beta 3. Good luck!