With headers you have limited heat in the intake crossover. The choke coil takes forever to heat up(if at all).
In post 65 here there's a pic of a secondary lockout arm. Yours is missing in your first pic. You should see it when your choke is full on. If it's missing in the linkage it can cause binding.
http://www.hotrodders.com/forum/roch...-190558-5.html