Since it's vacuum-operated, it could be the diaphragm too. I had some vacuum-operated CV carbs in an old motorbike and even a pinhole in the diaphragm would screw up the slide opening.
You can check the idle timing easy enough in the driveway, but the secondaries would really have to be checked under load, so if y'all want to take stuff to fix it out there, I would go with springs and a diaphragm, at least, (and assuming the diagnosis is correct.)
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