It doesn't sound like a choke problem to me ,I think your return spring has gotten weak and its not going back to idle.I haven't worked on one of those for many years so if I'm wrong and the spring is strong enough I would suggest getting a Chilton's manual for about 20 bucks and it will show you how to adjust the choke as there are many different areas to look at.Good luck to you,that's a sweet old car for sure.