New carb linkage idle problem

[69er]

I overhauled the 390 in my 69 F-250 and installed a new (rebuilt) 2 bbl Autoline carburetor. The problem is that when it's running the linkage is sticky and won't return to the dashpot very easily to idle down. When the motor is not running it works fine. It's well lubricated. Any thoughts on this?