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Well, all you can do is get this powerhead syncronized properly and try again. Pull the carbs apart and inspect the low speed jets if problems persist after proper syncronization. The pictures you posted look as though the butterflies are closed. But, don’t forget to disconnect the link between the two carbs and retest, just in case the linkage is preloaded open.
You still have the carbs from the damaged powerhead, perhaps you could try those as well. Keep in mind that the jet drive and conventional outboard are completely different animals, the original carbs are probably jetted much differently for this application. The one big difference between the carbs is that the old 140 uses a conventional choke, the newer jet drive uses the electric primer. So, you will have to transfer the primer valve and plumbing over also. The carb to intake gaskets are different also, the older gaskets don’t have a hole for the primer hose to spray…
You can’t tell much by revving the engine up in neutral, even though this jet drive doesn’t really have a neutral. And yes, the position of the throttle cam linkage will make a difference….
Good luck, sure hope I am wrong about that older powerhead. Don’t forget to do a compression test…