This usually means that you are running your engine "rich". You should "lean" it out slowly and watch the temperature so that you dont "lean" it out to far.
Nitros will always spit a little bit of unburnt oil out of the exhaust unless it is excessively lean. They should never get hot enough to burn the castor and synthetic oils in the fuel.
On the other hand, if it is spitting unburnt fuel (will have a distinctive tangy smell) then it is too rich, most likely on the HSN. I had this problem at first when I was new to nitro RC, but I fixed it. If it's just after break in you shouldn't start leaning it until about 10 tanks or so after break in.
i broke my car in already but i didnt go through 10 tanks yet. thanks alot though for the tips. i though my HSN was to much. do you think my LSN needs adjusting too?