O.K., I am not trying to confuse things here. But if one can't depend on the tac readings to set the engines for max performance then how do you know it is running to lean, should that happen. I am just trying to figure this out because I did have someone "tune" one of my O.S.46Fxi's and now it is dead, it was ran way to lean. Now I know it was ran to lean, but at the time I did not have any experience with it. Not that I am experienced now either.