[makrie]

I just purchased a 65 TBird. It came with a re-manufactured Autolite/Ford/Motorcraft 4100 carburetor and a spare. The pictures are of the spare but both have the same issue as I've had the carburetor off the car twice diagnosing this issue.

Specifically what is supposed to close the primary side butterflies? There is a coiled spring around the primary shaft but on either carb the spring only provides pressure for about half the rotation. The shaft from the accelerator pump brings it closer to fully closed but is not intended to hold it there. As I found the car delivered to me, the throttle shaft was pre-tensioned to close the butterfly with the accelerator rod... however according to the 64-65 shop manual this adjustment is for accelerator pedal height, not to close the primary.

What I found is not a lack of tension from the spring but a limit to the rotation. There are built in stops on the primary shaft which limit the spring assist to 90 degrees. That said in the first set of pics the rotation is far short of closure and these shafts appear to install only one way. I seem to be missing something but not sure what it could be.

I've included pics are of the carb with butterflies closed by hand against the warm idle stop (normal position); a view with the butterflies partially open at the point the coiled spring just engages; and a view of the shop manual where it describes in the text (not shown) how to adjust pedal height. Pictures of the shaft off the carb shows the spring in its unwound position against the first stop. The other with my hand forcing the shaft to turn against the second stop

Thank you for your time and expertise!