Tuning an engine is about its performance not its temp. The temp is a good way to gauge where you are with your tune but you cannot set an engine purely by the temp because of the example above. I do the majority of my tuning by sound. An engine running well sounds good and when its out of tune it will sound bad and the sounds different lean or rich. What your looking for is an engine that sounds good and still blows smoke. For me the smoke gets hard to see going around the track but I can always hear it.