I believe a 4133 S AFB has a weighted air door, not a spring controlled air door.
Doug
You are correct, it is a weighted air door. We are headed out for a test drive, I'll check back in with some data.
I honestly figure someone had a recipe for this common 575cfm AFB that came on many 383's and 440's.
All the AFB I've seen except some of the early 273 AFB, they didn't have any thing above the venturi
![confused confused](/ubbthreads/images/graemlins/custom/confused.gif)
, have weighted doors. Only the AVS and Thermoquad carbs. have the spring loaded doors
As far as having a decent tune up for todays fuel and the different altitudes and weather conditions, your probably going to need EFI to get that done