vacuum source?

[backrodebob]

not knowing much about flatheads and learning as I go, can someone identify this hole in intake manifold? looks like a vacuum source and possibly even a vacuum leak if not being used? and if so best way to seal?

 

[19Fordy]

Could that hole relates to the heat riser? Look here:
https://www.google.com/search?q=fla...GlGoFHRICBeIQ9QF6BAgDEAE#imgrc=wt4-u-8NkL2C1M

Here's some interesting reading.
https://fordbarn.com/forum/showthread.php?t=153993&showall=1

 

[51 MERC-CT]

Poke a wire into the hole to see what path it takes.
If it shows up at the heat riser port, tap a suitable size for a screw to plug it.

 

[TerryOH]

That hole, if that is truely what it is, is over the exhaust port which brings warm air to the base of the Carb. Most likely for an automatic choke. The brass fitting with the hose connector barb would appear to be manifold vacuum.