Mystery air intake

[dwmcompton]

I have a '73 Series III. I replaced the carburetor last week and noticed what I think is a missing hose or cap on an air intake tube on top of the manifoldjust in front of the carburetor. Can somebody please tell me what the function of this small air intake is? I'm pointing to it in this series of photos. When I cover that intake with my finger the engine runs slightly better. It feels like it should either be capped or should have a tube attached running to another place. Any help would be greatly appreciated.

12720 12721 12722

[lumpydog]

It looks like someone added an extra vacuum take-off port. Maybe to feed an instrument/gauge. Maybe to allow ad-hoc vacuum reading/testing from a hand-held gauge from time to time. Regardless, leaving it open will reduce the engine vacuum and impact the way the engine runs and will compromise the vacuum assist braking. Good vacuum is critical and air leaks like that are bad.

It looks like that same fitting has another port that runs to something else (I see a hose), so you should just blank off the open port. You will notice the engine runs WAY better and your brakes work better.

[dwmcompton]

Thanks! the other hose goes up to the servo. I have been running it with that open tube blocked with a piece of rubber hose and screw, and it definitely runs better, but I just wanted to be certain that there shouldn't be a hose running from it to another place. Thanks again.