When you remove the carb from the vehicle, you disconnect the springs that hold the throttle closed. Therefore, the throttle will flop wide open with the carb off the vehicle.

When installed, it MUST have the throttle return springs connected, or it will flop open with disastrous results.

 

I agree that you want an external throttle return spring for safety.
I believe that these carbs also had an offset throttle butterfly disc on the throttle shaft axis that would tend to close with air rushing past it into the engine. The slightly larger butterfly half would be towards the air horn.

 

Many years of Mopars with flatheads had that design. You lost the return spring and they went to full throttle. Wise to make sure the sling and connections were in good condition. Had it happen on the fifty Chrysler and dad on the 59 Plymouth. Both cases the engine was turned off and spring repaired.

 

Thank you for the reponses, very helpful. It seems there may have been some tinkering with the linkage and I'm missing some of the original hardware. I'lll focus on that and get that squared away with a new return spring.

 

Usually there were two return springs on older cars, at least in the 1960s and 70s. One was inside the other (concentric) in the applications I've seen. Redundancy.

 

Usually there were two return springs on older cars, at least in the 1960s and 70s. One was inside the other (concentric) in the applications I've seen. Redundancy.

60's was the first double springs. Good idea.