This may seem like a little simplistic, but did you check your throttle return spring. It may have lost it's strength. If you don't have one at all, I would recommend adding one.
Thought I should mention, my '69 originally had a 307. I still have the manifold, carburator, air cleaner, and I think I still have the valve covers if you are interested. The carb would have to be rebuilt of course.
[This message has been edited by GeorgeK (edited 07-01-99).]