Mick,
If our engines were only required to run at a constant speed and with a constant load, the carburettors could be set up to provide the best running conditions for that task. Unfortunately, we expect our engines to run at any speed from tickover to flat out, carry any load we might put on the bike, and then go uphill or down. To achieve this we may have to compromise on some of the settings, and the idling mixture is often set on the rich side to prevent flat spots as the throttle is opened. Providing you are happy with your bike's performance, I would leave well enough alone. Having said that, I have found that modern unleaded fuel can cause the engine to run weak on full throttle - to this end, I have increased my main jets by 10, reduced the slide cutaway by 1, and then compensated by lowering the needle. With the reduced slide cutaway the idling mixture can be weakened slightly without the risk of a flat spot.
Regards,
Eddie.