extremely high idle on start up

The black cover on auto choke has a little raised line on it.
If you look at the face of black cover you will see.
<-- rich l lean -->.
This is supposed to line up with a mark on alloy block it sits against.
Mark Near the top towards drivers side "about 1 o'clock".

If marks are out of alignment re-setting marks lined up together is a default setting.
set black mark by slightly loosen 3 small phillips screws.
their positioned around black cover at 2,6 & 10 o'clock and re-tighten.
see what happens.

having a think about your problem, is there a broken linkage on side of carby ?.
theory, with choke butterfly closed, higher vacume a linkage is being pulled onwards more than it should.