250 yz '02 jetting

I have a 250 yz '02 with a new top end. I think it runs ok but it develop at the end of the silencer that black unburned oil a little. I buied it in nov.'02 and because it was cold i thought that is normal, but now is a normal temperature outside. I'm riding in forest and hils and some on the track so is low-medium rpm 70% , 30% high rpm. I'm riding at ~2000 ft high most of the time. I don't feel is too rich and the mixture is 30:1. Should i go 40:1 ? Or is it normal because most of the time i ride it in the first half of RPM ? Is it still to rich? Thank you for any answer.

Thank you Faded, i will play a little with the jetting.With 40:1 i know i will have more fuel in the same volume of mixture but also less oil so maybe less splooge or should go with 30:1 to be shure not to damage the enginne?