There are so many factors that can effect tuning. Humidity/temperature and altitude for a few. I see you live in Australia so... and I must admit I'm not sure about your climate. If the temperature variations are fairly large between morning and afternoon this could cause a click or two of tuning adjustment. Cool air is more dense then warmer air. Thus when the air is cooler you need less volume to get the same amount of Oxygen molicules required for combustion so you can run a little richer. More air means more fuel to mix with it. At higher altitudes and hot air conditions when the air is less dence you will need a leaner needle setting.