I think that may be the twin carb idle sync/balancing adjustment screw. My memory of adjusting SU carbs is rather vague and I'm away from my old manuals at the moment, so until Planetman Eric or one of our other PV/Amazon gurus gets a chance to see this and give you a better response, I'll point you in a few directions.

There were assorted Stromberg SU carbs used in the early PV (444/544), Amazon (110/120) and 140/240 series bricks, the latter mostly in Europe, not North America. To aid you in identification try here https://www.skandix.de/en/documents/additional-information/volvo-stromberg-carburettor-typology/3000543/.

There is lots of technical information online for SU carbs, even a few Volvo green manuals. A good general place to start is the company's website still online here https://sucarb.co.uk/technical/. For Volvo specific information be sure to check out the https://ozvolvo.org/archive/. It's not indexed or even fully titled so you may need to spend some time poking around. If you haven't got it yet, you should probably also find yourself a copy of the 164 Haynes manual as a basic reference which will hopefully have a half decent section on carbs.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now