Just to clarify, the needles in cylinders 2 & 3 are LONGER than 1 & 4
and the reason for them being longer isn't to cool the innermost cyclinders it has to do with the air pressure through the carbs. As the air passes through the airbox into the carbs the path of least resistance is that of carbs 2 & 3, therefore petrol is attomised and drawn up easier than in carbs 1 & 4.
to match the same flow at the lower pressure of carbs 1 & 4 a bigger opening is required for a given throttle position, which is what the different needle lengths and tapers replicate.
It's strange then that all the aftermarket jet kits make them all the same length

maybe they are just concerned with full throttle max power than drivability.
I've looked into this at great depth as it's always stumped me on why the carbs are different, nice to finally find an answer I'm happy with so thought I'd share