http://www.rchobbies.org/engine-tuning.htm
check that link out and read it carefully, it has alot of good info for learning to tune a motor correctly. i wouldnt say it was a lack of oil issue, i would say its too lean. the colder the temps get outside, you will lose a tune from the last time you run it becaue the air is more dense and you have to richen it up a bit to make up for that.