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59096 perhaps some more tuning in need. Verify valve clearances, synch with a reliable, precise manometer and finish with properly setting the pilot screws, engine hot, each side for highest RPM.
I don't believe it left the factory with, nor would I give up on solving your reported 4500RPM and full throttle anomalies until the above tasks have been completed.
When carbs were apart, you verified stock pilot/main jet sizes/correct needles?
No jets "hogged out" or otherwise incorrect size/type?
I do diaphragm replace on metal slides (much easier than plastic 30mm slides)
I believe same diaphragm as EX500, which I keep in stock, though Auz is a long ways away, unfortunately.