Very simply put; there's nothing to lose by running a few tanks through new engine, except some fuel, but probably something to gain. the old ringed engines definitly needed a reasonable break in to seat the rings and cylinder. Most engines today do not have rings but will benefit by a few tanks of fuel run through them at a varying rich to lean setting prior to putting them in the air. It will take that much just to tune them properly. I have 2 evo engines and think they are misleading the public by saying no break in required. Also I have found it necassary to remove the restriction on Evo throttle to properly tune. Once done though they are great running engines. Just as with most things we each have our own opinions, those are mine.