I'm a fair weather boater -- really fair, like between 65 and 75 (OK, maybe 60 and 80). Important thing for tuning, though, is that you have it in the water one way or another. In a barrel, the water is typically about 40F so it takes a while to get the motor up to temp. But that's about the only temperature consideration. Once the motor is at operating temp you're good to go. (Although ability to feel fingertips can be important too, I guess.)