Look like a Weber 32/36 DGV (Manual Choke). The screw at the bottom is the idle air/fuel mixture. It should have an idle jet top right (facing the carb from the wing) and another on the opposite side. These are easy to pop out and clean.
However on yours I think the engine side one has been replaced with the fuel cut off solenoid (the part with the blue/yellow wire). Would be worth checking that it's working OK (or remove it and replace with a standard idle jet = you'll need the idle jet 55 or 50, jet holder and O ring)
Be lovely to pop over to California one day (my Grandad would have built some of the ash frame on yours)
"Y mae dafad ddu ym mhob praidd"
1972 4/4, 1981 MGBGT, 1984 FLHT1340, 1980 XLH1000, 1990 ZX10
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