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Can you tell me what is the function of the hole in the bottom of the flange that bolts to the intake manifold? I assume it must not be blocked.
Thanks,

I'm trying to resist public indecency by the nature of your question.

let start with what you have.... M38, M38A1 or...?

you can visually cross-reference the "hole" upon the part in question, within this download:

link: http://www.willysmjeeps.com/downloads/YScarb.pdf



I'm having one of those days.....

M38A1 on left and M38 on right. Note M38 has only one port.


The M38 carb combines the vacuum signal with the semi circular groove to feed both vacuum chambers.

They are the manifold vacuum supply to the vacuum chambers of the metering rod diaphragm and the accelerator pump diaphragm.

Since you indicated yours has only one hole there you must have the M38 YS637S carb.

A little tip: One of the easiest ways to determine what a port/orifice is used for is to lightly blow air in it and see where it comes out.

Thanks, yes mine is similar to the M38 on the right. I was going to take a picture of it and post it for clarity. Now I won't have to.
Thanks again,