dont tune for temps tune for perfomance, my 18ss likes to run a little bit hot, but if you aadd some klotz benol to it, it brings the temps down alot, i usually raise the oil percentage fo my fuel by 2-3% and it really helps out on tuning and temps, but my 18ss liked to run around 270-280, then again i was running on crappy blue thunder fuel that was all synthetic, get some more castor oil in your fuel and it should help out ( also cut more air ventilation holes if there arent too many)