"Tim Wescott" WROTE:
I'd do a complete rebuild on the carb, just on general principals. If the
tube is that old, then the rest of the non-metal parts are that degraded,
too, and any fine passages may well be choked with varnish.

Seconded. I had a similar problem in the past, which turned out to be fixed
with a new gasket between the tank and the upper carb body. Spent weeks
fiddling with the thing before solving it with a fifty cent part.

Jon