Mattax,
""So my question is this whether the lean surge also occurs above the PV opening vacuum?""
- No it does not.

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""However when the PV does open, the AFR should not get suddenly leaner if the carb is already on the mains (even partialy). Check the AFR at 12" and 10". If its already around 16:1 or higher, then 16:1 at 9.5"vac at least makes sense. If AFR is richer at 10 and 12"Hg than at 9", then something is not right.* If its continuing to get leaner below the PV opening vacuum then the PV is probably not opening when it should be.""

- I will check that out once I get the carb back together.

Thank you for your response.