I doubt that it's the ignition if it only happens in that rpm range. I think that it's too lean, but it could also be rich. Installing a wide band oxygen sensor could confirm that. I would try one step richer idle jets and see what happens. Webers run off the idle circuit well past idle, and 2000 rpm may be the point of transition to the main circuit.
This is when it pays to have a mechanic that has a lot of Weber experince, and also may have extra jets floating around.
bye,

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Csaba
1972 280SEL 4.5, silver