Noobi,
Talking with Boni at Gas Gas during my trip to Sapin. He said the best carb setup for the 125 is to get rid of the 38 and got to a 36 for better overall power. He said the top end loss is not noticable, but the mid is much better. I didn't ask about the jetting as Spain has better quality fuel then the US. I will be on a 09 125 which is the same basic bike. So once I get it sorted I will report back.
Brian