You'll tend to go a little leaner in the summer because the air is less dense. Obsessive types may actually go down one step in the heat of the plug or reduce the nitro a little, but I don't bother with that. As for setting the low end, heat isn't going to affect it much, so get a good idle and transition and leave it alone. On all my engines, if they won't idle for at least 30 seconds and then go immediately to full throttle, I don't fly.