I think there may be another topic somewhere this may fit in but could Japan have offered to go to war against Germany after the fall of western Europe, in exchange for the UK and perhaps the Dutch East Indies, breaking the US embargos? Could Japan have offered more to the UK than the US?
Back to the original topic, if there were no (or fewer) US carriers in the Pacific in 1942 then the New Guinea campaign could have been quite different. As I mentioned in another topic, the Australian reaction to the raids on Darwin from 19 February 1942 was to concentrate on the defence of Darwin to the detriment of Port Moresby, the saving grace for new Guinea being the availability of US carrier based aircraft to back up the single RAAF squadron. No carriers, no help for Port Moresby and possibly a successful sea borne invasion, or at least less support for the defenders fighting along the Kokoda Track.
The pacific campaign was a close run thing in the early months with Japan proving to have not quite enough resources to fight US and the Commonwealth across multiple fronts. No US carriers could have seen the fall of New guinea, no ongoing fighting in New guinea would give them a better chance in Guadalcanal, this could have allowed them to better isolate Australia.
Overall effect I don't know but Japans entry into the war did see the withdrawal of Australian land forces from the Middle East and ensured they played no part in Italy or Western Europe, while once US forces were fully mobilised in the Pacific, US policy saw Australia perhaps playing a far less prominent role than they would have say in France. No US carriers would have perhaps seen a more prominent role for Australia in the Pacific.