The OE choke cap has a ring shaped paper gasket between it and the
carburetor body.  These paper gaskets have an annoying tendency to collapse
and get drawn inward to the point where they interfere with the operation of
the choke, i.e., they begin to interfere with the movement of the bimetal
spring inside the choke cap.  Before you spend a lot of time trying to
diagnose the choke, make sure that the gasket is ok.  It should be visible
all the way around the choke cap between the choke cap and the carburetor
body.  It it's not and there's a visible gap, then the gasket will need to
be replaced.  If the choke has never been worked on before, then the factory
rivets holding it to the carburetor body will need to be drilled out.  If
this is the case, then be sure to cover the carburetor to prevent metal
chips from getting into the engine.

Eric

The choke is not capable of raising the rpm that high. What is probably
happening is Frequency Solenoid Valve C is not supplying, or delaying,
the engine vacuum needed to allow the throttle to close beyond its
Start position.

My workaround was to route the throttle positioner hose to the vacuum
test port, where it receives vacuum at all times.

I do have a shop manual, and am located in Cedar Mill.
The two responses sound very informative. I will be looking at my
carburetor.