Dying Webber

[bill <pplusb@northlink.com>]

My '77 rdstr has a downdraft Weber.
At a stop, it may idle straight down to zero and stall, or it may hang
on to an idle for a short while before nose diving.
I've fiddled with mixture, although not too expertly, and have the idle
screw turned way up, to no avail.
This phenomenon can be more pronounced when cold.
I need help - anybody have any ideas??

TIA
Bill