I don't know if I got this from some where else or I made it up myself. My theory is that you can't over enrich the bike for starting. Therefor I set them to full on when starting the first time of the day, later in the day if the bike has sat an hour or even more I might use half enrichner. But for first start even on warm days I use full enrichner.
I want my bike to start with authority. No crank, crank, crank. My bike starts Immediately. Every time.
If I have to turn it over more than once I have probably done something wrong, like not setting the enrichners on full or the bike needs some little attention.